PDF creation is only possibly in TOM if you are running the program under FileMaker Pro.
While you always have the option of using a third-party print-to-pdf solution, the benefit of TOM's own PDF creation is that file names and paths are generated fully automatically and that thereby you can launch or find the PDF files from within TOM (e.g. auto-attach the invoice pdf to an e-mail).
Setting the path to the default pdf folders
Whenever you create a pdf document from an invoice, offer etc. TOM tries to store it in a specific folder for TOM documents.