How do Idetermine if a PDF file exists

I am writng a script to allow my users to combine up to 8 pdfs into the open document. The script needs to determine which of the 8 files are available and then insert them in a preset order.
The files are always in the same directory and are a branch name of the main file
EG Main_File.pdf
Then Main_File_A.pdf, Main_File_B.pdf, Main_File_D.pdf etc
As you will note Main_File_C.pdf was not listed as this may not have been created so I need my script to identify it is not there and skip over it.

I have tried palying with the catching the exception error on an app.opendoc() but it does not suit my purpose. I dont want the files to open just to know they are there.

Thanx in advance anyone who can Help
Mark Green