How Can I Use MD5 to Detect Modifications in PDF Files Processed with iTextSharp?

Leveraging MD5 for PDF Modification Detection with iTextSharp

Extracting text from image-heavy PDFs using iTextSharp can be problematic. However, MD5 checksums offer a robust solution for verifying if a PDF has been altered.

Generating the MD5 Hash

The System.Security.Cryptography.MD5 class provides the functionality to compute an MD5 hash. Here's how:

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

Comparing MD5 Hashes

The MD5 hash is a byte array. For easy comparison, convert it to a Base64 string:

<code class="language-csharp">var hash1 = Convert.ToBase64String(md5.ComputeHash(stream1));
var hash2 = Convert.ToBase64String(md5.ComputeHash(stream2));

if (hash1 == hash2)
{
    // Files are identical
}</code>

MD5 Hash as a Hexadecimal String

To represent the hash as a hexadecimal string, use BitConverter:

<code class="language-csharp">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>

This MD5 hashing technique ensures reliable detection of PDF modifications, even when other extraction methods prove unreliable.

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