Merging PDF Files in ASP.NET

I am using C# and asp.net

I have the following code to combine two PDF files.

This runs in debug mode. But it does not from the web client. What do I need to do to make this work? Thanks much in advance.

                String filePath = GlobalVar.excelSavedFilePath;
                inFileName  =  "input.pdf";
                appendFileName = "append.pdf";
                DirectoryInfo dirInfo = new DirectoryInfo(GlobalVar.excelSavedFilePath);
                outFileName = GlobalVar.excelSavedFilePath + "out1.pdf";


                Type AcrobatPDDocType;
                AcrobatPDDocType = Type.GetTypeFromProgID("AcroExch.PDDoc");
                Acrobat.CAcroPDDoc src = (Acrobat.CAcroPDDoc)Activator.CreateInstance(AcrobatPDDocType);
                Acrobat.CAcroPDDoc dest = (Acrobat.CAcroPDDoc)Activator.CreateInstance(AcrobatPDDocType);


                src.Open(filePath + inFileName);
                dest.Open(filePath + appendFileName);


                src.InsertPages(src.GetNumPages() - 1, dest, 0, dest.GetNumPages(), 0);
                src.Save(1, outFileName);
                src.Close();
                dest.Close();


                msg = "Merged";
                return msg;