How Can MD5 Checksums Verify the Integrity of Image-Only PDF Files?

Ensuring Image-Only PDF Integrity with MD5 Checksums

Extracting text from image-heavy PDFs can be difficult. To reliably verify if an image-only PDF has been altered, calculating its MD5 checksum is a robust solution.

MD5 (Message Digest Algorithm 5) is a cryptographic hash function generating a unique, fixed-size signature for any given data. Even a minor file change produces a completely different MD5 checksum.

Here's how to compute an MD5 checksum in .NET using the System.Security.Cryptography.MD5 class:

<code class="language-csharp">using (var md5 = MD5.Create())
{
    using (var stream = File.OpenRead(filename))
    {
        return md5.ComputeHash(stream);
    }
}</code>

The resulting hash is a byte array. For easier comparison, convert it to a string using hexadecimal representation:

<code class="language-csharp">static string CalculateMD5(string filename)
{
    using (var md5 = MD5.Create())
    {
        using (var stream = File.OpenRead(filename))
        {
            var hash = md5.ComputeHash(stream);
            return BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
        }
    }
}</code>

By comparing the MD5 checksums of two PDFs, you can instantly detect any alterations. This is especially valuable when regularly downloading PDFs and needing to confirm their integrity without relying on text-based verification.

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