pdf.js has had 26 pull requests merged in the last month. 5,622 additions and 6,991 deletions. That's just in the project directly, not in the dependencies.

Since it's such a quickly evolving project, I wondered where form support is up to. https://github.com/mozilla/pdf.js/issues/7613

Form support is not complete. Seems like it required quite a rewrite to get the foundation in a good place to finish it off.

Are there rendering bugs? Yes. See plenty here: https://github.com/mozilla/pdf.js/issues

Of course, Acrobat also has PDF rendering bugs, and other various bugs apart from the security issues mentioned (their JavaScript implementation for example).

As for printing... browsers aren't even good at printing HTML. The best browser for printing is based on the old Opera software(PrinceXML), and Safari is probably second. Remember the Apple display system used to be based on PDF rendering... and they do a lot with CUPS and graphic designers.

However, printing PDFs on many browsers can go directly to the printer or the OS (which mostly all support rendering PDFs directly now).