Can I convert a PDF into FrameMaker

I fairly often deal with this situation by saving as plain text and then tagging the results as MML for easy import. No need to faff around joining up lines in paragraphs, for one thing; and this approach also lets me put in placeholder paragraphs for graphics and tables, and mark italic/bold if need be. (or mark, say, code-strings as italic and then apply the correct character style in FM)

A pity FM won't (as far as I know) read CALS tables …

Another approach might be to open the PDF in Acrobat Pro DC and save as a DOCX. You can then import the DOCX into FrameMaker and post edit it.

Quality of the result depends on the PDF and how it was created, of course.

re: Is there a free, simple tool available for converting a PDF file into a reasonable FrameMaker file?

PDF is basically device-independent Postscript, and not a editable document format. Anything that purports to convert a PDF into editable mark-up is going to have to make a lot of guesses about structure, flow, and how to optimally recover images. Tables could be a particular problem, as they are likely to be just text strings at page coordinates, fenestrated by vector lines (i.e. not really tables)

When I had to do this in the past, I'd copy out the text as plain-text, and use Illustrator to deconstruct pages for optimal image recovery (keeping vectors as vectors, and grabbing rasters at native res).

Tables might be just saved as EPS from IL, and imported as-is.

Yep, essentially, you're re-creating the document.

If the PDF has certain forms of security, this all gets a lot harder.