Can Images in a Local Markdown File Be Converted into Internal Items During Import?

The main difference between print (PDF) and screen is not size but the concept of “fixed canvas”: a PDF (as well as Word etc) is made up of pages of a fixed size, a screen can show potentially infinitely long documents in arbitrary zoom factors.
But since PDF is a vector format, you can scale it without losing quality (within bounds when downscaling). That works also for the fonts, of course.