I’m not looking for a full PDF editor. Only to do tasks like merging and splitting PDFs, removing pages, or creating a PDF from a bunch of images.
https://www.ilovepdf.com is very handy, but I don’t like the idea of uploading my documents to them, especially if they have sensitive data.
I’ve used pdf.tocgen to add chapter headings into pdfs. It was the only thing I found that could do any pdf table of contents editing at all period. I think it can do a few other things though.