Print preview add watermark

[myJOB1122]

Hi
my problem:

1. How to do Print preview add watermark
2. Please give my a demo
   thanks very much!

[Snuffleupagus]

That's not a use-case that this library is intended for; note https://github.com/mozilla/pdf.js#pdfjs-

PDF.js is a Portable Document Format (PDF) viewer that is built with HTML5.

For future reference: When opening an issue, please provide all of the information requested in https://github.com/mozilla/pdf.js/blob/master/.github/ISSUE_TEMPLATE.md