Please note that the original app was Xournal [1]. The one you link is a rewrite of the orignal (in C++) and is called Xournal++. [1] https://xournal.sourceforge.net/. - Source: Hacker News / 3 months ago

I do the using Xournal [1] which is tailor-made for creating annotations. It leaves the PDF as is, saving your edits to a sidecar file (*.xoj) which when loaded pulls in the original PDF. It exports edited documents to 'real' PDFs with selectable text etc. [1] https://xournal.sourceforge.net/ (packaged by most distributions). - Source: Hacker News / over 1 year ago

If you don't mind the signature being raster (not vector), I've used Xournal for this in the past. It's extremely lightweight and easy. Just open the PDF file with Xournal, draw the signature, and then export it to PDF (Control + E). This will not rasterise the PDF itself (to the best of my knowledge), but rather just superimposes a layer containing your signature on top of the original PDF. Source: about 2 years ago

Xournal++ exists since 2013. Maybe you typoed and by your comment about abandoning you were referring to Xournal without the ++? The Xournal website even suggests to try Xournal++. Source: over 2 years ago

Xournal works pretty well for me on GNU/Linux. You just have to turn on the "Legacy PDF Export" option. Source: almost 3 years ago

You can see an example in the main screenshot on noteship.com (the entry "Apartment Hunting > Tiny Studio" has 3 sub-entries that are external PDFs that were moved into the project. Source: over 2 years ago

Good point, sorry about that. Here is the link: https://noteship.com/. Source: over 2 years ago