I have been using another product (Intaglio for Macintosh) to produce vector graphics files and then export them as PDF files to distribute and send to a printer. This program does not work with macOS Big Sur, there is no updated version, and the company appears to have gone out of business. Can Illustrator or another Adobe product open and edit PDF files of this sort so I can edit (modify) the PDF files I have saved from this other program?
Importing a pdf into Illustrator produces mixed results as far as editability is concerned. If the pdf contains vector objects then they usually can be altered in Illustrator. However, many pdfs have flattened raster content which cannot be edited in Illustrator. Also many pdfs import in with multiple clipping masks which may need to be released for more easy editing. If there is live text in the pdf then it will usually come into Illustrator as point type with multiple insertion points—which means that the text is not flowable and thus not easily edited. The bottom line is that Illustrator is not designed as a pdf editing program so there is no guarantee. I would suggest getting a trial version of Illustrator at https://www.adobe.com/products/illustrator/free-trial-download.html?sdid=JRSIH&mv=search&ef_id=Cj0KC.... You can experiment for seven days before you decide if you want to subscribe.