Currently, saving a PDF from Illustrator keeps the saved PDF open in Illustrator. If you edit the file that is still open, you're editing the PDF and not the native Illustrator file. It is difficult to see that you're working in PDF other than just remembering that Illustrator does this (when other Adobe apps do not), and/or to look at the extension on the file tab.

Feature request is to change this function so that Illustrator remains open in the same Illustrator file format instead of switching to working in the saved PDF via Illustrator. This would be similar to InDesign's function of saving PDF, where saving a PDF just saves a PDF copy out of InDesign, and you remain in the native InDesign file. Thanks!