Renaming a pdf based on text within the pdf

This may be possible using a Bridge script, however I am guessing that an Adobe Acrobat script or another third party tool would probably be better as it could look into the underlying PDF structure.

I would need to see at least two different sample PDF files to see if they had consistent internal structure or metadata that could be used for renaming.

Some inexpensive third party tools that do what you are looking for are listed toward the end of this blogpost:

Prepression: Splitting PDF Files to Variable File Names

That may be possible, but may not. Asking a qestion is often not enough. There are experienced people who can do much about things they never particulary were involved into. So by methods they know but firstly had to use for something else like it. You should then give more inofmations like where is that exact invoice number and images form before/after effect.