C# PDF File Protect Library
How to add, generate, remove PDF file permission with owner password using c# .net

        #region apply pdf document permission settings with password
        internal static void applyPermissionSettings()
        {
            String inputFilePath = @"C:\demo.pdf";
            String outputFilePath = @"C:\demo_with_settings.pdf";

            // Create a password setting object with user password "Hello World".
            PasswordSetting passwordSetting = new PasswordSetting("Hello World");

            // Set encryption level to AES-128.
            passwordSetting.Level = EncryptionLevel.AES_128bit;

            // Printing is allowed.
            passwordSetting.IsPrint = true;

            // Print with high-resolution.
            passwordSetting.IsHighReso = true;

            // Document is allowed to be changed.
            passwordSetting.IsModify = true;

            // Annotation is allowed.
            passwordSetting.IsAnnot = true;

            // Form filling is allowed.
            passwordSetting.IsFillForm = true;

            // Content extraction is allowed.
            passwordSetting.IsExtract = true;

            // Copying is allowed.
            passwordSetting.IsCopy = true;

            // PDF document assembling is allowed.
            passwordSetting.IsAssemble = true;

            // Add password to the file.
            PDFDocument.AddPassword(inputFilePath, outputFilePath, passwordSetting);
        }
        #endregion