Probably the simplest approach is to set the file to read-only via the file system. Short of a custom Acrobat plug-in, I don't think there's another way to do this in Acrobat...
Well, there is at least one other way. It involves setting up a special template-based FDF file. When the FDF is launched, the PDF gets created on-the-fly from template pages from one or more PDFs. The user can Save or SaveAs the resulting PDF without affecting the original(s). There are certain limitations to this approach and it can get a bit complicated, but it's possible.
Well, there is at least one other way. It involves setting up a special template-based FDF file. When the FDF is launched, the PDF gets created on-the-fly from template pages from one or more PDFs. The user can Save or SaveAs the resulting PDF without affecting the original(s). There are certain limitations to this approach and it can get a bit complicated, but it's possible.
George