PDFs, Templates, and misery

A friend of mine is about to work for a new company and has asked me help him with the technical side. He'll be doing home maintenance, and they want him to upload photos along with an invoice for the work, and a 'bid' document that is essentially the same thing, but needs to be submitted separately.

They have sent him an Invoice.pdf file that is really neat. He types the information he needs to enter into the file, and then hits the button at the bottom of the PDF that the author created to save the completed form as a new pdf. The original template is retained (as it's read-only), and he has the completed PDF form ready to send to his employer. Basically, the perfect little template.

He doesn't have a Bid template however. I've spent many hours trying to edit the Invoice.pdf to change the two references to the word 'Invoice' to 'Bid', but that doesn't work. Doing so breaks the form - reopening it leads to the message:
This document enabled extended features in Adobe Reader. The document has been changed since it was created and use of extended features is no longer available. Blah blah blah...

I gave up with that approach and tried to create a new PDF from scratch and duplicate the template. Ultimately this approach would work, but being a complete newb with PDF editing software, I'm ready to give up.

So far I've used Foxit, Nitro PDF Professional and Abode X Pro. I haven't had success with any of them.

My friend Does have Microsoft Word (2007?). Can Microsoft word be used to create a template in a similar manner? Is there a good way to literally change two words in the PDF without Abode Reader detected it's been changed? Is there any other alternative I haven't thought of?