Thank you very much for considering Aspose.
I have noticed that your PDF files contain PDF Forms, so you can use ConcatenateForms method as shown in the following code snippet:
I have tested the files using above sample and the concatenation was successful.
Aspose.Pdf.Kit.PdfFileEditor editor = new Aspose.Pdf.Kit.PdfFileEditor();
editor.ConcatenateForms(“EGA_Met_Business_Class_Fax_Cover_Sheet.pdf”, “EGA_Authorization_Form.pdf”, “output1.pdf”);
editor.ConcatenateForms(“output1.pdf”, “COMPDISC-ID_LiveCycle_030909.pdf”, “output2.pdf”);
editor.ConcatenateForms(“output2.pdf”, “COMB-89216-HI.pdf”, “output3.pdf”);
If you have any further questions or find some other issue, please do let us know.