Flatten PDF

Flattening means several quite different things for PDFs. At least two of them apply specifically to your case, and with printing there is too much at stake to guess; I would advise you to ask the following question:

 

"We've been told that flattening could mean

- removing transparency effects

- combining layers into one

- making sure comments and form fields are part of the background (probably not relevant).

Please let me know which kind(s) of flattening you need - transparency and/or layers.

Also, do you need a particular version of PDF (e.g. PDF 1.4) or of PDF/X (e.g. PDF/X-3)? It would be helpful to know why you have this requirement."