Xournal++ is my go to. It has a few quirks to get used to, but once you do it's quite functional. Biggest thing to watch out for is exporting and overwriting

Xournal++ is my go to. It has a few quirks to get used to, but once you do it's quite functional. Biggest thing to watch out for is exporting and overwriting the source file. It will usually let you, but it often blanks out the source and loses your changes. So just make sure to export with a different filename than the original is. If you accept the default suggestion, it will work fine. It's also made to be used well with wacom tablets, so if you have one of those you can make use of it in xournal++. The older "Xournal" (no ++) is mostly functional but also dead, so I would go with Xournal++.