Program.cs

using System;
using DevExpress.Pdf;
using System.Diagnostics;
using DevExpress.Office.DigitalSignatures;
using System.Linq;
using DevExpress.Office.Tsp;

namespace PdfDocumentProcessor
{
    class Program
    {
        static void Main(string[] args)
        {
            ApplySignatures();
            Process.Start(new ProcessStartInfo("SignedDocument.pdf") { UseShellExecute = true });
        }

        public static void ApplySignatures()
        {
            //Load a document to sign
            using (var signer = new PdfDocumentSigner("Document.pdf"))
            {
                //Specify the name and location of the signature field
                var signatureFieldInfo = new PdfSignatureFieldInfo(1);
                signatureFieldInfo.Name = "SignatureField";
                signatureFieldInfo.SignatureBounds = new PdfRectangle(20, 20, 150, 150);
                signatureFieldInfo.RotationAngle = PdfAcroFormFieldRotation.Rotate90;
                
                //Create a timestamp
                ITsaClient tsaClient = new TsaClient(new Uri(@"https://freetsa.org/tsr"), HashAlgorithmType.SHA256);

                //Create a PAdES PKCS#7 signature
                Pkcs7Signer pkcs7Signature = new Pkcs7Signer("Signing Documents/certificate.pfx", "123", HashAlgorithmType.SHA256, tsaClient, null, null, PdfSignatureProfile.PAdES_BES);

                //Apply a signature to a new form field created before
                var cooperSignature = new PdfSignatureBuilder(pkcs7Signature, signatureFieldInfo);

                //Specify an image and signer information
                cooperSignature.SetImageData(System.IO.File.ReadAllBytes("Signing Documents/JaneCooper.jpg"));
                cooperSignature.Location = "USA";
                cooperSignature.Name = "Jane Cooper";
                cooperSignature.Reason = "Acknowledgement";

                //Apply a signature to an existing form field
                var santuzzaSignature = new PdfSignatureBuilder(pkcs7Signature, "Sign");

                //Specify an image and signer information
                santuzzaSignature.Location = "Australia";
                santuzzaSignature.Name = "Santuzza Valentina";
                santuzzaSignature.Reason = "I Agree";

                // Specify signature appearance parameters:
                PdfSignatureAppearance signatureAppearance = new PdfSignatureAppearance();
                signatureAppearance.SetImageData("Signing Documents/SantuzzaValentina.png");
                signatureAppearance.SignatureDetailsFont.Size = 12;
                signatureAppearance.SignatureDetailsFont.Italic = true;
                signatureAppearance.ShowDate = true;
                signatureAppearance.ShowReason = true;
                santuzzaSignature.SetSignatureAppearance(signatureAppearance);

                //Create a new signature form field:
                var signatureFieldInfo1 = new PdfSignatureFieldInfo(1);
                signatureFieldInfo1.Name = "SignatureField1";
                signatureFieldInfo1.SignatureBounds = new PdfRectangle(200, 200, 250, 250);

                //Create a document level time stamp:
                PdfTimeStamp pdfTimeStamp = new PdfTimeStamp(tsaClient);

                //Apply this time stamp to the form field:
                var timeStampSignature = new PdfSignatureBuilder(pdfTimeStamp, signatureFieldInfo1);

                //Add signatures to an array
                PdfSignatureBuilder[] signatures = { cooperSignature, santuzzaSignature, timeStampSignature };

                //Sign and save the document
                signer.SaveDocument("SignedDocument.pdf", signatures);
            }
        }
    }
}