If you happen to be on macOS, the Preview app does an absurd number of things to PDFs, and it does it well. To be honest I'm always surprised it isn't highlighted more by Apple, it's a great tool that pretty much always just works. You can split files, join them, rotate, add signatures, drawings, annotations, redact sections, etc. The feature list is long, especially considering that by the name of the application you'd think it could just preview files, not edit them.

> to be honest I'm always surprised it isn't highlighted more by Apple

Probably because its not so intuitive, I have to google how to use some of the advanced features of Preview.

I often use PDF Sam (basic) and usually it works quite well and is offline.

https://pdfsam.org/

A really nice, stand-alone command line tool is pdfcpu.

https://github.com/pdfcpu/pdfcpu

Looks great, but my partner needs something more convenient.

It needs to be web based and work on desktop/mobile.

You can simply use poppler-utils on your on computer? It's a collection of commandline tools for PDF-manipulation. More information can be found here: https://pypi.org/project/poppler-utils/

KDE’s Okular. Works on Linux, Windows and macOS.

If you’re on already macOS, Preview already has you covered.

Does it need to be a self hosted web based tool or do you just need PDF software? If the latter I find PDF Expert to be powerful and nice to use.

I use pdftool.org which I saw on HN a while back

Edge is surprising decent for marking up PDFs.