PDF is not editable after uploading it to RT

We use RT 4.4 with a MySQL database. When we upload a PDF to a ticket, that PDF cannot be updated in its original location on the desktop. I am wondering if this is an affect as a result of how RT manages its file uploads or if this is a limitation with Adobe Pro. I haven’t had this experience with any other file. Has anyone else had this experience?

What error does Adobe give you when you try to update your local copy of the PDF?