Example 15: Merge 2 existing PDF files - C# Copy 
Add a reference in your Visual Studio project to docConverter library.
To do this:
        a. On the Project menu, click Add Reference;
        b. On the COM tab, locate docConverter Library and then click Select;
        c. Click OK in the Add References dialog box to accept your selections.
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10  |   Neevia.docConverter DC = new Neevia.docConverter();
  int RVal = DC.mergePDF(@"c:\users\public\file1.pdf", @"c:\users\public\file2.pdf", @"c:\users\public\out.pdf");
  DC = null;
  if (RVal != 0) {
    MessageBox.Show("There was an error merging the PDFs !!!");
  } else {
    MessageBox.Show("Done !!!");
  }
 |