One of the greatest advantages of using PDF files for proofing, as opposed to JPEGs, is that text remains as editable text and it never loses its crispness. This is of special importance when you are working across different platforms (Mac/Windows/Linux) and need to make sure that text in a file looks right every time.
As explained in Chapter 42, "Working in a PDF in Acrobat," Acrobat makes a copy of the font file, embeds it within the PDF itself, and uses its own rendering engine to display text with it. This ensures that text will always render and print as text, with crisp edges and no pixelation.
Recall that Acrobat allows only minor text editing. There's a reason for that. Acrobat is not a page layout program or a word processor. Acrobat is a program that you should use to optimize files created in other programs. Yes, there are exceptions like creating PDF files from a scanner or using the Designer (more about that in Chapter 46, "Using Adobe Designer (Windows CS2 Suite Only)"), but the main objective remains the same.