Applied automatically to a copy of your \documentclass preamble at compile time — the source you pasted above is never modified. The diagonal watermark sits transparently behind the whole page (low opacity keeps it from competing with the text); the corner stamp instead lives in the header/footer margin so it never overlaps body text — it's skipped automatically if your source already defines its own header/footer. Font-family and watermark settings add their own packages, so if your source already loads a conflicting one, the setting simply takes precedence.