Can Illustrator open a PDF following PDF/X-4 standard and interpret it correctly?

You will see when you are in the Save As > PDF dialog that setting the Standard to "None" turns on the checkbox for "Preserve Illustrator editing capabilities."

Setting the Standard to "PDF/X-4" and that box is grayed out and can't be selected.

Because a PDF _can_ preserve certain functions (Layers, Effects) of Illustrator, embedding this data into the PDF violates the very strict PDF/X standard.

So, short answer, as Ton said, is yes, you can open a PDF/X-4 file. And you can Save As > PDF and specify compliance with PDF/X-4. But is it not X-4 while it is open in Illustrator, and will no longer be X-4 is you simply open and Save.

(NB: in CC 2019, while the PDF preset specifies PDF/X-4:2010, Illustrator actually uses PDF/X-4:2007, if that matters for anyone. See this thread: https://community.adobe.com/t5/illustrator/my-adobe-pdf-presets-don-t-show-up-in-illustrator-cc/m-p/10862034#M162083 )

Hi Julie–Liang

As far as i know, there's absolutely NO guarantee (or promise) that AI shows/interprets an existing PDF/X-4 file correctly (or as wished). It also depends how and with which software-tool the PDF was created.

If you wanna have AI functionalities kept, choose this option in the Export. But then, its no PDF/X-4 file anymore, at least in theory…