How to Encrypt and Password-Protect a PDF using C# .NET Framework

Coding workflows to secure our PDF documents can be a time-consuming challenge. Thankfully, with a free low-code solution, we can avoid the bulk of that work and come up with consistent, reliable results.

Using the ready-to-run C# code further down the page, we can easily take advantage of a free API to encrypt and password-protect our PDF documents. We can set user & owner passwords with simple request parameters, and we can even choose from two distinct encryption key lengths (options are 128-bit RC4 encryption & 256-bit AES encryption; the latter is default).

We can start structuring our API call by installing the SDK. We can run the following command in our Package Manager console to install via NuGet:

Install-Package Cloudmersive.APIClient.NET.DocumentAndDataConvert -Version 3.4.2

Next, before we call our function, let’s grab a free-tier API key to authorize our API calls. This will allow a limit of 800 API calls per month with no additional commitments.

Now let’s copy the below code and customize our request:

using System;
using System.Diagnostics;
using Cloudmersive.APIClient.NET.DocumentAndDataConvert.Api;
using Cloudmersive.APIClient.NET.DocumentAndDataConvert.Client;
using Cloudmersive.APIClient.NET.DocumentAndDataConvert.Model;

namespace Example
{
    public class EditPdfEncryptExample
    {
        public void main()
        {
            // Configure API key authorization: Apikey
            Configuration.Default.AddApiKey("Apikey", "YOUR_API_KEY");

            var apiInstance = new EditPdfApi();
            var inputFile = new System.IO.FileStream("C:\\temp\\inputfile", System.IO.FileMode.Open); // System.IO.Stream | Input file to perform the operation on.
            var userPassword = userPassword_example;  // string | Password of a user (reader) of the PDF file (optional) 
            var ownerPassword = ownerPassword_example;  // string | Password of a owner (creator/editor) of the PDF file (optional) 
            var encryptionKeyLength = encryptionKeyLength_example;  // string | Possible values are \"128\" (128-bit RC4 encryption) and \"256\" (256-bit AES encryption).  Default is 256. (optional) 

            try
            {
                // Encrypt and password-protect a PDF
                byte[] result = apiInstance.EditPdfEncrypt(inputFile, userPassword, ownerPassword, encryptionKeyLength);
                Debug.WriteLine(result);
            }
            catch (Exception e)
            {
                Debug.Print("Exception when calling EditPdfApi.EditPdfEncrypt: " + e.Message );
            }
        }
    }
}

Just like that, we now have free low-code solution to streamline our PDF security workflows.