PdfSharp.Pdf.PdfDocument doc = new PdfSharp.Pdf.PdfDocument();

var securitySettings = doc.SecuritySettings;
securitySettings.OwnerPassword = "dummypassword"; // <<---- will encrypt links
securitySettings.PermitModifyDocument = false;
securitySettings.PermitAssembleDocument = false;
securitySettings.PermitExtractContent = true;
securitySettings.PermitAnnotations = false;
securitySettings.PermitFormsFill = false;
securitySettings.PermitFullQualityPrint = true;
securitySettings.PermitAccessibilityExtractContent = true;

doc.AddPage();

doc.Pages[0].AddWebLink(new PdfSharp.Pdf.PdfRectangle(new PdfSharp.Drawing.XRect(200,500,200,200)), "http://www.example.com/");

doc.Save("test.pdf");