Can MD5 Checksums Detect PDF File Modifications?

Use MD5 checksum to verify PDF file integrity

When PDF files containing only image content cannot extract text, MD5 checksums provide a reliable way to detect whether the file has been modified.

Calculate MD5 checksum using System.Security.Cryptography.MD5

Using the System.Security.Cryptography.MD5 namespace, the steps to calculate the MD5 checksum are as follows:

<code class="language-csharp">using System.Security.Cryptography.MD5;

// 打开PDF文件进行读取
using (var stream = File.OpenRead(filename))
{
    // 创建MD5哈希对象
    using (var md5 = MD5.Create())
    {
        // 从文件流计算哈希值
        return md5.ComputeHash(stream);
    }
}</code>

Compare hash results

The generated byte arrays can be compared directly or converted to base64 encoding for easier processing. To output the hash value as a hex string:

<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 regularly calculating and storing MD5 checksums, you can effectively detect whether any modifications to PDF files have occurred between downloads.

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