Thanks for the question. We generally do try find answers to all of our questions or at least point you in the right direction. You have only given the most general information, no code, and I don't have any way to verify the issue on an account because your support center ID does not link to any known account.
However, I did a little bit of looking around and hopefully this post about the issues of uploading PDF files with PHP will be exactly what you need to make it work. Make sure to read the last response, it has the information that I think you need to make it work.
If you need further assistance, can you please provide a link or information to a related account (if you are hosting with InMotion Hosting). Error messages or anything else that we can use to help troubleshoot the problem.