Protect Base64 PDF with a password using iText 7

Using iText 7, we can define two passwords: a user password and an owner password. A pdf that is encrypted with an owner password can be opened by every one who receives the document. The owner password is there to define permissions (for instance: the document can be viewed, but not printed). If a pdf is encrypted using a user password, everybody who knows the user password can open the file. There is no username, only a user password.

Nuget Package:

Install-Package itext7 -Version 7.1.7

Import Following packages:

using iText.Kernel.Pdf;
using System;
using System.Text;
using System.IO;

Source Code

public static string EncryptPDFwithPassword(string pdfBase64, string passwordUser, string passwordOwner)
{
    var encryptedBase64 = string.Empty;
    var srcBytes = Convert.FromBase64String(pdfBase64);
    var userPassword = Encoding.ASCII.GetBytes(passwordUser);
    var ownerPassword = Encoding.ASCII.GetBytes(passwordOwner);

    PdfReader reader = new PdfReader(new MemoryStream(srcBytes));
    WriterProperties props = new WriterProperties()
            .SetStandardEncryption(userPassword, ownerPassword, EncryptionConstants.ALLOW_PRINTING,
                    EncryptionConstants.ENCRYPTION_AES_128 | EncryptionConstants.DO_NOT_ENCRYPT_METADATA);

    using (var memoryStream = new MemoryStream())
    {
        PdfWriter writer = new PdfWriter(memoryStream, props);
        PdfDocument pdfDoc = new PdfDocument(reader, writer);
        pdfDoc.Close();
        encryptedBase64 = Convert.ToBase64String(memoryStream.ToArray());
    }

    return encryptedBase64;
}

Use it as:

EncryptPDFwithPassword("base64pdf-without-any-prefixes", "niceuser", "niceowner");

References:

https://www.nuget.org/packages/itext7/
https://itextpdf.com/en/resources/faq/technical-support/itext-7/how-protect-pdf-username-and-password
https://itextpdf.com/en/resources/faq/technical-support/itext-7/how-protect-already-existing-pdf-password