Sometimes works ...
I had a similar problem with some legal documents (happened to be a Company Memorandum of Association) which I had to update and was only available in PDF format.
Opened the PDF in Adobe Acrobat version XI - then click on "File", click on "Save As" and save the document as a text file.
This only seems to work with some documents (maybe those without any security settings) and it only saves "pure" text (ie. any images do not appear so it might not worked on scanned FAX images). The formatting is often a dog's breakfast. But it did save me quite a lot of tedious re-typing, albeit at a the cost of some editing effort.
FWIW - your mileage might differ!