As I've probably cited before, the adage is "being given a .pdf and having to produce a source file is like being given a bowl of chicken soup and being asked to produce the chicken".

If you're a provider with the right to edit the content of these .pdf documents, you ought to be able to request source files instead of having to make them yourself: much more efficient for you, and less worry (that things are being accidentally changed by a complicated conversion process) for the original author. This is how we prepare and deliver user manuals for our products, which vendors can then customise as required.