File Content Extraction 25.4
Filter SDK .NET Programming Guide

# Start Using the Filter API

To use the .NET Filter SDK, open your project in Visual Studio and add a reference (Project > Add Project Reference) to the library `filter_dotnet.dll`, which can be found in the `bin` directory. Then add the following statement to your program code.

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    using KeyView.Filter;

## Create a Session

To use the Filter API, first create a session:

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    using (Session session = new Session(binDir, license))
    {
        // Configure the session and open a document
    }

`binDir` should be a `string` that holds the location of the Filter SDK binaries, and `license` should be a `string` that holds your license key.

The `Session` class implements the `IDisposable` interface, so you can enclose your use of the session in a `using` block to ensure that resources are automatically freed when no longer required.

To use the Filter API in a multi-threaded application, create a unique session on each thread and do not share a session or document between threads.

## Open a Document

A `Document` object provides access to the data within a file, including the file format, text, metadata, and any subfiles. Obtain a `Document` object from a file or stream by calling the `Open()` method on your `Session`. For example:

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    string inputFilePath = "InputFile.docx";
    using (Document myDoc = session.Open(inputFilePath))
    {
        // Use the document object to detect the file format, filter text,
        // access metadata and extract subfiles
    }

## Determine the Format of a Document

You can find the format of a document by using the `Info()` method on a `Document` object. For example:

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    using (Document myDoc = session.Open(inputFilePath))
    {
        Console.WriteLine("File class: " + myDoc.Info().DocClassName());
        Console.WriteLine("File format: " + myDoc.Info().DocFormat().ToString());
        Console.WriteLine("Description: " + myDoc.Info().Description());
        Console.WriteLine("File version: " + myDoc.Info().Version().ToString());
    }

## Filter a Document

To filter a document and write the text to a file or stream, call the `Filter()` method on a `Document` object. For example:

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    using (Document myDoc = session.Open(inputFilePath))
    {
        try
        {
            // Filter to a file
            myDoc.Filter(inputFilePath + ".filtered.txt");

            // Alternatively, filter to a stream
            // using (FileStream fs = File.Create(inputFilePath + ".filtered.txt"))
            // {
            //     myDoc.Filter(fs);
            // }
        }
        catch (KeyViewException e)
        {
            Console.WriteLine($"{e.Message}");
        }
    }

## Access Metadata

You can access document metadata through the `Metadata()` method on a `Document` object. For example:

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    using (Metadata metadata = myDoc.Metadata())
    {
        foreach (var element in metadata) using (element)
        {
            // Process the metadata element
        }
    }

## Extract Subfiles

You can iterate over subfile information using the `Subfiles()` method on a `Document` object. Each element returned by the iterator contains information about the subfile, and a method that you can use to extract it:

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    foreach (Subfile file in myDoc.Subfiles()) using (file)
    {
        Console.WriteLine($"Subfile {file.Index()}, size: {file.Size()}");

        if (file.GetSubfileType() != SubfileType.Folder)
        {
            string outputPath = GenerateOutputPath(file);
            file.Extract(outputPath);
        }
    }

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Version 25.4 | Last updated October 2025

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Product: File Content Extraction 25.4

Topic Title: Start Using the Filter API