Thank you for your post.
Currently, iOS 5 does not allow the overwriting of files, so a new file is created each time. If the file name is identical to an existing file name, then the number 2 is appended to the file name. Therefore, when you create the PDF file, make sure it is a unique name. Some customers append the date to the file name to ensure uniqueness.
Let me know if you need additional clarification.