Can I watermark an EPUB as well as a PDF?

Yes — the ARC Watermarker stamps both EPUB and PDF. Which you send depends on your reviewer:

• EPUB — best for reviewers reading on e-ink e-readers and reading apps, where reflowable text is comfortable.
• PDF — best for reviewers reading on a computer or tablet, or who want the exact print layout.

Many authors offer both and let each reviewer pick. Load whichever format(s) you want to distribute and generate personalized copies of each.