Add page numbers to a PDF. The file stays in this tab.
A sketch of the corner, not your pages. Bottom center is the usual spot.
"of 12" counts every page in the file, including a cover you skip. White ink is for a dark page. I can't see the page color.
The numbering runs in your browser. The PDF is not sent to a server, and you don't sign in. That is the difference from the free Adobe tool, which uploads the file.
No. Opening the network panel will show no request carrying your file. The page can load once and then work offline. A locked, password-protected PDF is refused, because opening it would mean handling the password.
Yes. The number is drawn on top of each page. Text that is already in the file is left as it is. If a page was saved sideways, the number is turned so it reads with the page.
A signature will no longer verify, because the file changed. Fillable fields usually survive, but check them if the form matters. Try one file before you batch a stack.
Yes. Set "Skip first pages" to 1 and start at 1. Page one of the file stays blank. The next page prints 1. The "of" number is still the full page count, so a 12-page file with a blank cover ends on "Page 11 of 12".