Note: Add a reference in your project to PDFsignNET To do this:   a. On the Project menu, click Add Reference;   b. On the .NET tab, locate PDFsignNET and then click Select;   c. Click OK in the Add References dialog box to accept your selections.

  Neevia.PDFsign NVsign = new Neevia.PDFsign();
  int retVal;

  NVsign.PDFEncrypt = true;
  NVsign.PDFEncryptionType = "rc4";
  NVsign.PDFOwnerPassword = "owner";

  // p - document printing is denied
  // e - disable extraction of text and graphics
  NVsign.PDFPermissions = "pe";

  retVal = NVsign.EncryptPDF(@"c:\in.pdf",@"c:\out.pdf");

  if (retVal != 0) {
     MessageBox.Show("Error code = " + retVal.ToString());
  } else {
     MessageBox.Show("Done");
  }