decoding_pdf-streams-itextsharp

how can i decode streams to endstream objects in pdf document easily with c sharp?

Decoding streams to endstream objects in a PDF document using C# can be done with the help of libraries like iTextSharp or PdfSharp. Here's a basic example using iTextSharp:

Install iTextSharp: You can install the iTextSharp library via NuGet Package Manager in Visual Studio.
Code Example:

csharp

using System;
using System.IO;
using iTextSharp.text.pdf;
using iTextSharp.text.pdf.parser;

class Program
{
    static void Main()
    {
        string pdfPath = "path/to/your/document.pdf";
        using (PdfReader reader = new PdfReader(pdfPath))
        {
            for (int i = 1; i <= reader.NumberOfPages; i++)
            {
                PdfDictionary pageDict = reader.GetPageN(i);
                PdfArray contentArray = pageDict.GetAsArray(PdfName.CONTENTS);
                if (contentArray != null)
                {
                    foreach (PdfObject item in contentArray.ArrayList)
                    {
                        PRStream stream = (PRStream)PdfReader.GetPdfObject(item);
                        byte[] data = PdfReader.GetStreamBytes(stream);
                        string decodedStream = System.Text.Encoding.UTF8.GetString(data);
                        Console.WriteLine(decodedStream);
                    }
                }
            }
        }
    }
}

This code will read the PDF document, iterate through each page, and decode the stream objects to text.

Explanation:

PdfReader: Reads the PDF document.
GetPageN: Retrieves the dictionary of a specific page.
GetAsArray: Gets the content array of the page.
GetPdfObject: Retrieves the stream object.
GetStreamBytes: Decodes the stream bytes to a string.

Feel free to tweak the code to suit your specific needs.

i want to do these without any third party api

Got it! You can decode streams in a PDF document using C# without any third-party libraries by working directly with the PDF file format. Here's a basic example:

Read the PDF File: Open the PDF file and read its content.
Parse the PDF Structure: Identify and extract the stream objects.
Decode the Streams: Convert the stream bytes to readable text.

Here's a simple example:

csharp

using System;
using System.IO;
using System.Text;

class Program
{
    static void Main()
    {
        string pdfPath = "path/to/your/document.pdf";
        byte[] pdfBytes = File.ReadAllBytes(pdfPath);

        // Find the "stream" and "endstream" keywords
        string pdfText = Encoding.UTF8.GetString(pdfBytes);
        int streamIndex = pdfText.IndexOf("stream");
        int endStreamIndex = pdfText.IndexOf("endstream");

        while (streamIndex >= 0 && endStreamIndex >= 0)
        {
            // Extract the stream content
            int streamStart = streamIndex + "stream".Length;
            int streamLength = endStreamIndex - streamStart;
            string streamContent = pdfText.Substring(streamStart, streamLength).Trim();

            // Decode the stream content (assuming it's plain text for simplicity)
            byte[] streamBytes = Encoding.UTF8.GetBytes(streamContent);
            string decodedStream = Encoding.UTF8.GetString(streamBytes);
            Console.WriteLine(decodedStream);

            // Find the next stream and endstream
            streamIndex = pdfText.IndexOf("stream", endStreamIndex);
            endStreamIndex = pdfText.IndexOf("endstream", streamIndex);
        }
    }
}

This code will read the PDF file, find the "stream" and "endstream" keywords, and decode the stream content. Note that this example assumes the stream content is plain text. In reality, PDF streams can be compressed or encoded in various ways, so you may need to handle different decoding methods.

It looks like you're working on extracting stream data from a PDF. Let's refine your code a bit and make it more robust. Here’s an improved version that handles stream extraction without relying on third-party APIs:

csharp

int streamIndex = pdfText.IndexOf("stream");
int endStreamIndex = pdfText.IndexOf("endstream", streamIndex);

while (streamIndex >= 0 && endStreamIndex >= 0)
{
    // Extract the stream content
    int streamStart = streamIndex + "stream".Length;
    int streamLength = endStreamIndex - streamStart;
    string streamContent = pdfText.Substring(streamStart, streamLength).Trim();

    // Decode the stream content (assuming it's plain text for simplicity)
    byte[] streamBytes = Convert.FromBase64String(streamContent);
    string decodedStream = Encoding.UTF8.GetString(streamBytes);
    Console.WriteLine(decodedStream);

    // Find the next stream and endstream
    streamIndex = pdfText.IndexOf("stream", endStreamIndex + "endstream".Length);
    endStreamIndex = pdfText.IndexOf("endstream", streamIndex);
}

Some key points to consider:

Base64 Decoding: The above code assumes the stream content is base64 encoded. Adjust the decoding method if your stream content uses a different encoding.
Error Handling: Incorporate error handling to manage exceptions and unexpected cases gracefully.
Performance: Large PDFs can be slow to process using string manipulation. For better performance, consider using a PDF parsing library designed for such tasks.

Decoding PDF stream objects is complex because streams can use various encoding mechanisms such as compression (e.g., Flate, LZW, RunLength) and encryption. Here’s how to handle decoding streams in a PDF document using pure C#:

Decoding Schemes for PDF Streams

PDF objects support various encoding schemes, including:

FlateDecode (zlib/Deflate compression).
LZWDecode (LZW compression).
RunLengthDecode (Run-length encoding).
ASCIIHexDecode (ASCII hex encoding).
ASCII85Decode (ASCII base-85 encoding).
CCITTFaxDecode (CCITT fax compression, typically for monochrome images).
JBIG2Decode (JBIG2 compression for bi-level images).
DCTDecode (JPEG compression for images).
Crypt (Encryption decoding).

Steps to Decode PDF Streams Without Third-Party APIs

Parse the PDF File
Use byte-level operations to find and extract the stream and endstream sections.
Extract Metadata for Decoding
Streams in PDF documents often include metadata in the dictionary before the stream keyword. Look for /Filter entries to determine the encoding.
Implement Decoding Methods
Depending on the /Filter entry, implement appropriate decoding logic. For example:
- For FlateDecode: Use zlib decompression.
- For ASCIIHexDecode: Convert hexadecimal string to bytes.
- For RunLengthDecode: Implement run-length decoding logic.
Combine the Steps
Process the PDF file and decode the streams based on the identified filters.

Example: Extracting and Decoding PDF Streams

Here’s a pure C# implementation that handles basic stream extraction and FlateDecode decoding:

csharp
using System;
using System.IO;
using System.IO.Compression;
using System.Text;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string pdfPath = "path/to/your/document.pdf";
        byte[] pdfBytes = File.ReadAllBytes(pdfPath);
        string pdfText = Encoding.ASCII.GetString(pdfBytes);

        // Regex to find "stream" and "endstream"
        Regex streamRegex = new Regex(@"stream[\r\n]+(.*?)endstream", RegexOptions.Singleline);
        MatchCollection matches = streamRegex.Matches(pdfText);

        foreach (Match match in matches)
        {
            string streamContent = match.Groups[1].Value.Trim();

            // Decode the stream (assuming FlateDecode)
            try
            {
                byte[] compressedData = Encoding.ASCII.GetBytes(streamContent);
                byte[] decodedData = FlateDecode(compressedData);
                string decodedText = Encoding.UTF8.GetString(decodedData);
                Console.WriteLine(decodedText);
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error decoding stream: {ex.Message}");
            }
        }
    }

    // FlateDecode (zlib decompression)
    static byte[] FlateDecode(byte[] compressedData)
    {
        using (var input = new MemoryStream(compressedData))
        using (var output = new MemoryStream())
        {
            using (var deflateStream = new DeflateStream(input, CompressionMode.Decompress))
            {
                deflateStream.CopyTo(output);
            }
            return output.ToArray();
        }
    }
}

Key Points

Filter Detection:
Modify the code to parse the /Filter entry in the stream’s dictionary. For example:
```
csharp

if (dictionary.Contains("/Filter /FlateDecode"))
{
    // Apply FlateDecode
}
```
Encoding Variants:
Implement decoding for other encodings (e.g., ASCII85Decode, RunLengthDecode) as needed.
Error Handling:
Streams may be corrupted or use unsupported filters. Add error handling to skip problematic streams.
Performance Optimization:
For large PDFs, process the file in chunks instead of loading the entire file into memory.

Challenges

Complex Filters: Some streams use multiple filters (e.g., /Filter [/FlateDecode /ASCII85Decode]), requiring chained decoding.
Encrypted Streams: Handling encrypted streams requires parsing the PDF’s security settings.
Binary Streams: Streams may contain binary data (e.g., images), so not all decoded data will be readable text.

This example provides a starting point for working with PDF streams directly in C#. Expand the implementation to handle additional decoding schemes and metadata parsing as needed

The FlateDecode method you provided is a good start, but there are a few things to consider that might be causing issues:

Stream Padding: PDF streams often have extra padding or whitespace around the "stream" and "endstream" keywords. Make sure you're correctly identifying the start and end of the stream data.
Compression Headers: The compressed data might include additional headers that need to be removed before decompression. For example, the zlib format includes a 2-byte header.
Error Handling: Ensure you have proper error handling in place to catch any exceptions during decompression.

Here's an updated version of your FlateDecode method that takes these factors into account:

csharp

using System;
using System.IO;
using System.IO.Compression;

static byte[] FlateDecode(byte[] compressedData)
{
    // Remove the first two bytes (zlib header)
    if (compressedData.Length > 2 && compressedData[0] == 0x78)
    {
        compressedData = compressedData[2..];
    }

    using (var input = new MemoryStream(compressedData))
    using (var output = new MemoryStream())
    {
        try
        {
            using (var deflateStream = new DeflateStream(input, CompressionMode.Decompress))
            {
                deflateStream.CopyTo(output);
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Decompression failed: {ex.Message}");
        }
        return output.ToArray();
    }
}

This version removes the first two bytes of the compressed data if they match the zlib header (0x78). It also includes basic error handling to catch any exceptions during decompression.

you can extract chunks of every page in a PDF file using C# without any third-party libraries. Here's a basic example to get you started:

Read the PDF File: Open the PDF file and read its content.
Parse the PDF Structure: Identify and extract the content streams for each page.

Here's a simple example:

csharp

using System;
using System.IO;
using System.Text;

class Program
{
    static void Main()
    {
        string pdfPath = "path/to/your/document.pdf";
        byte[] pdfBytes = File.ReadAllBytes(pdfPath);

        // Convert the PDF bytes to a string
        string pdfText = Encoding.UTF8.GetString(pdfBytes);

        // Find the "obj" keyword to identify objects
        int objIndex = pdfText.IndexOf("obj");
        while (objIndex >= 0)
        {
            // Find the "endobj" keyword to identify the end of the object
            int endObjIndex = pdfText.IndexOf("endobj", objIndex);
            if (endObjIndex < 0) break;

            // Extract the object content
            string objContent = pdfText.Substring(objIndex, endObjIndex - objIndex + "endobj".Length);

            // Check if the object is a page object
            if (objContent.Contains("/Type /Page"))
            {
                // Find the "stream" and "endstream" keywords to extract the content stream
                int streamIndex = objContent.IndexOf("stream");
                int endStreamIndex = objContent.IndexOf("endstream");
                if (streamIndex >= 0 && endStreamIndex >= 0)
                {
                    int streamStart = streamIndex + "stream".Length;
                    int streamLength = endStreamIndex - streamStart;
                    string streamContent = objContent.Substring(streamStart, streamLength).Trim();

                    // Decode the stream content (assuming it's plain text for simplicity)
                    byte[] streamBytes = Encoding.UTF8.GetBytes(streamContent);
                    string decodedStream = Encoding.UTF8.GetString(streamBytes);
                    Console.WriteLine(decodedStream);
                }
            }

            // Move to the next object
            objIndex = pdfText.IndexOf("obj", endObjIndex);
        }
    }
}

This code will read the PDF file, find the "obj" and "endobj" keywords to identify objects, and extract the content streams for each page. Note that this example assumes the stream content is plain text. In reality, PDF streams can be compressed or encoded in various ways, so you may need to handle different decoding methods.

PDFs can save annotations, markups, comments, and other interactive elements, and these are typically stored in structured objects within the PDF, but not directly as part of the stream/endstream object that holds raw data like text or images. Instead, the markup-related information is stored in annotation objects in the PDF's page dictionary or interactive forms.

How Markups and Comments Are Stored in PDFs

Annotations, markups, and comments are stored in PDF dictionaries and are referenced in a page's /Annots array. Here are some details:

Annotation Dictionary (/Annot):
- This dictionary specifies the properties of an annotation, such as its type, position, content, and appearance.
- Common annotation types include:
  - /Text: For comments or notes.
  - /Highlight: For text highlights.
  - /Underline: For underlining text.
  - /Popup: For pop-up comments.
  - /Widget: For form fields.
Stream for Appearance (stream/endstream):
- Some annotations, like highlights or custom graphics, use appearance streams (/AP) to define their visual representation. These streams are stored as stream/endstream objects and contain the graphical content for the annotation.

Structure:

A page's dictionary contains an /Annots array that references annotations.

Example:

plaintext
/Annots [
  << /Type /Annot /Subtype /Text /Contents (This is a comment) /Rect [100 100 200 200] >>
  << /Type /Annot /Subtype /Highlight /Rect [150 150 250 250] >>
]

Text and Markup Content:
- The actual text of a comment (e.g., a note or popup) is stored in the /Contents key of the annotation dictionary.
- Additional appearance settings (like font, color, or graphics) may be stored in /AP as streams.

Can Markups and Comments Be in `stream/endstream`?

While the content of the annotations (like the text of a note or comment) is typically stored in plain text within dictionaries, the visual representation of markups and comments (like highlighted text or custom graphics) might be stored in stream/endstream objects. These are often used for:

Custom Appearances (/AP):

Visual elements associated with an annotation are defined in an appearance stream.

Example:

plaintext
/AP <<
  /N << /Subtype /Form /Length 123 >>
>>
stream
... (graphics operators defining the appearance) ...
endstream

Annotations That Use Graphics:
- Highlighting, underlining, or strikethrough annotations often include an appearance stream to define their graphical representation on the page.

Extracting Comments and Markups

To extract comments and markups from a PDF in C#:

Parse the /Annots array from the page's dictionary.
For each annotation:
- Read its /Subtype to determine the type of annotation.
- Extract the /Contents for textual data.
- Extract and decode /AP streams if present for graphical representations.

Example: Parsing Annotations in C#

Here's how to identify and extract comments and markups from a PDF:

csharp

using System;
using System.IO;
using System.Text;

class Program
{
    static void Main()
    {
        string pdfPath = "path/to/your/document.pdf";
        byte[] pdfBytes = File.ReadAllBytes(pdfPath);
        string pdfText = Encoding.ASCII.GetString(pdfBytes);

        // Find annotation dictionaries
        if (pdfText.Contains("/Annots"))
        {
            int annotsIndex = pdfText.IndexOf("/Annots");
            Console.WriteLine("Annotations found:");

            // Simplistic parsing to demonstrate concept
            int start = pdfText.IndexOf("[", annotsIndex);
            int end = pdfText.IndexOf("]", start);
            string annotArray = pdfText.Substring(start, end - start);

            Console.WriteLine(annotArray);

            // Decode individual annotations (example: /Contents)
            if (annotArray.Contains("/Contents"))
            {
                int contentsStart = annotArray.IndexOf("/Contents");
                int contentsEnd = annotArray.IndexOf(")", contentsStart);
                string comment = annotArray.Substring(contentsStart, contentsEnd - contentsStart + 1);
                Console.WriteLine($"Comment: {comment}");
            }
        }
        else
        {
            Console.WriteLine("No annotations found.");
        }
    }
}

Summary

Markups, comments, and annotations are primarily stored in annotation dictionaries (/Annots) within the PDF structure.
Appearance streams (stream/endstream) are used to define the visual representation of annotations, such as highlights or custom graphics.
Extracting this information involves parsing the PDF's page dictionaries and decoding annotation properties and streams as needed.

Exhaustive List of Annotation Types in PDFs

Annotations in PDFs, as specified in the PDF specification (ISO 32000), include the following types:

Text Annotations (/Text):
For comments or notes.
- Keys: /Contents (text of the note), /Rect (position), /Popup (associated pop-up window).
Link Annotations (/Link):
For hyperlinks.
- Keys: /A (action), /Rect (position), /URI (URL).
Highlight Annotations (/Highlight):
Highlights text.
- Keys: /QuadPoints (coordinates of highlighted text), /AP (appearance stream).
Underline Annotations (/Underline):
Underlines text.
- Keys: /QuadPoints, /AP.
Squiggly Annotations (/Squiggly):
Draws squiggly lines under text.
- Keys: /QuadPoints, /AP.
StrikeOut Annotations (/StrikeOut):
Strikes out text.
- Keys: /QuadPoints, /AP.
Popup Annotations (/Popup):
Display pop-up windows associated with other annotations.
- Keys: /Parent (associated annotation), /Rect.
Widget Annotations (/Widget):
Used for form fields.
- Keys: /FT (field type), /T (field name), /V (value), /AP.
FreeText Annotations (/FreeText):
For writing text directly on the page.
- Keys: /Contents, /Rect, /DA (default appearance).
Line Annotations (/Line):
Draws a straight line.
- Keys: /L (coordinates), /BS (border style), /AP.
Square and Circle Annotations (/Square and /Circle):
For rectangular or elliptical shapes.
- Keys: /Rect, /BS, /AP.
Polygon and PolyLine Annotations (/Polygon, /PolyLine):
Draws shapes with multiple vertices.
- Keys: /Vertices (coordinates of vertices), /AP.
Ink Annotations (/Ink):
Allows freehand drawing.
- Keys: /InkList (array of points), /AP.
Stamp Annotations (/Stamp):
Adds a stamp to the page.
- Keys: /Name (stamp type), /Rect, /AP.
FileAttachment Annotations (/FileAttachment):
Embeds a file as an annotation.
- Keys: /FS (file specification), /Rect.
Sound Annotations (/Sound):
Attaches a sound file.
- Keys: /Sound (sound stream), /AP.
Movie Annotations (/Movie):
Embeds a video.
- Keys: /Movie (movie data), /AP.
3D Annotations (/3D):
Embeds 3D content.
- Keys: /3D (3D data stream), /AP.
Redact Annotations (/Redact):
Marks content for redaction.
- Keys: /QuadPoints, /AP.

Extracting Annotations Using Plain C# (Through Stream Handling)

Here's how to extract annotation details manually:

Read the PDF File: Open and read the raw bytes of the PDF file.
Locate the Page Dictionary: Search for /Page objects to find the /Annots key.
Parse the /Annots Array: Extract the objects referenced in the /Annots array.
Parse Annotation Dictionaries: Identify the /Subtype key to determine the type of annotation and extract related keys like /Contents, /Rect, /AP, etc.

Implementation

csharp

using System;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string pdfPath = "path/to/your/document.pdf";
        byte[] pdfBytes = File.ReadAllBytes(pdfPath);
        string pdfText = Encoding.ASCII.GetString(pdfBytes);

        // Locate pages and annotations
        MatchCollection pageMatches = Regex.Matches(pdfText, @"/Type\s*/Page\s*.*?/Annots\s*\[(.*?)\]");
        foreach (Match pageMatch in pageMatches)
        {
            Console.WriteLine("Found Page with Annotations:");

            // Extract annotation references
            string annotArray = pageMatch.Groups[1].Value;
            MatchCollection annotMatches = Regex.Matches(annotArray, @"\d+\s+\d+\s+R");
            foreach (Match annotMatch in annotMatches)
            {
                Console.WriteLine($"Annotation Reference: {annotMatch.Value}");

                // Locate annotation dictionary
                string annotRef = annotMatch.Value.Trim();
                Match annotDictMatch = Regex.Match(pdfText, $@"{annotRef}.*?<<.*?>>", RegexOptions.Singleline);
                if (annotDictMatch.Success)
                {
                    string annotDict = annotDictMatch.Value;
                    Console.WriteLine($"Annotation Dictionary: {annotDict}");

                    // Extract annotation details
                    Match subtypeMatch = Regex.Match(annotDict, @"/Subtype\s*/(\w+)");
                    Match contentsMatch = Regex.Match(annotDict, @"/Contents\s*\((.*?)\)");
                    Match rectMatch = Regex.Match(annotDict, @"/Rect\s*\[(.*?)\]");

                    if (subtypeMatch.Success)
                        Console.WriteLine($"  Type: {subtypeMatch.Groups[1].Value}");
                    if (contentsMatch.Success)
                        Console.WriteLine($"  Contents: {contentsMatch.Groups[1].Value}");
                    if (rectMatch.Success)
                        Console.WriteLine($"  Rect: {rectMatch.Groups[1].Value}");
                }
            }
        }
    }
}

Explanation

Regex for Pages and Annotations:
- Locate /Page objects and extract /Annots references.
Find Annotation References:
- Extract object references (X Y R) in the /Annots array.
Parse Annotation Dictionaries:
- Use the object reference to locate the corresponding dictionary.
- Extract details like /Subtype, /Contents, /Rect.
Output Annotation Details:
- Display extracted details for each annotation.

Challenges

Encoding/Decoding: Some annotation content might be compressed (e.g., FlateDecode).
Complex Structures: Parsing nested dictionaries can be challenging without a full PDF parser.
Streams: Appearance streams (/AP) may require handling PDF graphic operators.

For handling streams manually, you'd need to decode compressed streams (using algorithms like Flate or ASCII85).

Parsing all kinds of PDF streams requires implementing a variety of decoding mechanisms to handle the compressed and encoded data. The exhaustive list of stream filters and decoding methods you'll need to implement is based on the PDF specification (ISO 32000). Below is a comprehensive guide.

Exhaustive List of PDF Stream Filters

Each filter represents a specific compression or encoding mechanism applied to PDF stream data:

FlateDecode:
- Uses the zlib/deflate compression algorithm.
- Decodes binary or text data.
- Often paired with /Predictor for image data.
- Implementation: Use System.IO.Compression.DeflateStream in C#.
ASCIIHexDecode:
- Encodes binary data as hexadecimal text.
- Decodes text by converting hex pairs back to binary.
- Implementation: Convert hex strings to bytes and handle the end character (>).
ASCII85Decode (Base85):
- Encodes binary data in ASCII using 85 characters.
- Decodes by reversing the Base85 encoding.
- Implementation: Decode Base85 to binary bytes.
LZWDecode (Lempel-Ziv-Welch):
- A lossless compression algorithm.
- Commonly used in older PDFs.
- Implementation: Requires a custom LZW decoder or leveraging third-party libraries.
RunLengthDecode:
- A simple form of compression using run-length encoding.
- Encodes runs of identical bytes.
- Implementation: Decode by interpreting byte sequences according to RLE rules.
CCITTFaxDecode:
- A compression method for monochrome (1-bit) image data.
- Common in scanned documents.
- Implementation: Use libraries or write a CCITT Group 3/Group 4 decoder.
JBIG2Decode:
- A highly efficient compression method for bi-level images.
- Often used in scanned PDFs.
- Implementation: Requires advanced decoding tools, often handled by external libraries.
DCTDecode:
- Encodes image data using JPEG compression.
- Decodes JPEG streams.
- Implementation: Use libraries like System.Drawing or SkiaSharp to decode JPEG images.
JPXDecode:
- Encodes image data using JPEG2000 compression.
- Decodes JPEG2000 streams.
- Implementation: Use specialized JPEG2000 libraries.
Crypt (Optional):
- Handles encrypted streams.
- Decoding depends on the security handler and encryption keys.
- Implementation: Requires handling PDF security and key decryption.
Other Filters:
- FDFDecode: For Forms Data Format streams.
- SubFilters: Used for Digital Signatures (/SubFilter key).

Steps for Parsing and Decoding Streams

Identify Filters:
- Streams have a /Filter entry in their dictionary.
- Example: /Filter [/FlateDecode /ASCII85Decode].
Decode Streams in Order:
- Filters are applied in sequence, so decode them in the order listed in the /Filter array.
- Example: A stream with /Filter [/FlateDecode /ASCII85Decode] requires decoding ASCII85 first, then Flate.
Handle Parameters:
- Streams may have additional parameters under the /DecodeParms key.
- Example: /Predictor, /Colors, /BitsPerComponent.
Implement Decoders:
- Write or use libraries for each decoding mechanism.
- Ensure compatibility with common parameter settings.
Decompress Content:
- After decoding, interpret the stream content (text, images, etc.).

Example: Handling FlateDecode in C#

csharp
using System;
using System.IO;
using System.IO.Compression;

class Program
{
    static byte[] FlateDecode(byte[] input)
    {
        using (var inputStream = new MemoryStream(input))
        using (var deflateStream = new DeflateStream(inputStream, CompressionMode.Decompress))
        using (var outputStream = new MemoryStream())
        {
            deflateStream.CopyTo(outputStream);
            return outputStream.ToArray();
        }
    }

    static void Main()
    {
        byte[] compressedData = File.ReadAllBytes("path/to/compressed_stream.dat");
        byte[] decompressedData = FlateDecode(compressedData);

        Console.WriteLine("Decompressed Data: ");
        Console.WriteLine(System.Text.Encoding.UTF8.GetString(decompressedData));
    }
}

Challenges and Recommendations

Complex Filter Chains:
- Streams often use multiple filters (e.g., /ASCII85Decode /FlateDecode).
- Decode in the exact sequence specified.
Advanced Decoders:
- Implementing LZW, CCITT, JBIG2, and JPX decoding can be complex. Use third-party libraries like:
  - PDFsharp: Handles basic PDF decoding.
  - iText7: Comprehensive PDF library.
  - SkiaSharp: For image decoding (DCT, JPX).
Encryption:
- For encrypted PDFs, handle decryption using the /Crypt filter and security handler.
Testing:
- Use sample PDFs with known filters to validate each decoder.

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