Firefox can add text/drawings to PDFs
mozilla.org
mozilla.org
There is also https://simplepdf.eu
It is way too convoluted anywhere else.
Does it add the text as comments, or as "actual PDF content"? Comments are fine in most cases (and always when printing the document for archaic ceremonies involving ink and paper signatures), but I've had a few cases where I'd wished there was an easy way to add "actual text" in Apple's Preview.app.
I'm no longer concerned about exploits from sketchy PDFs.
But it cannot print a web page. And the pdf viewer is a usability disaster.