Draw is a super underappreciated piece of software imo. It's not quite Publisher, not quite Inkskape, but something in between. I'm not sure what people use it for, but I used it in college to make diagrams for all sorts of projects. LibreOffice's equation input is great, too.
My preferred Open-Source-Software for diagrams is draw.io (https://app.diagrams.net/). Works great, locally and online and runs on pretty much any system while offering everything I need and allowing a crazy amount of customisation.
That's good to know. I like Inkscape but its page handling still needs a bit more work.
I'd describe Draw's page handling as "intuitive," if not "sophisticated." You won't get Inkscape's most powerful features, but MS Office-like "stupid simplicity" is the result.
LibreOffice has pretty cool support for working with PDFs in general. (Tangential) There's a "hybrid PDF" export option in LibreOffice that lets you embed ODF metadata into the PDF file. When you open the exported file in LibreOffice again you get everything back -- dynamic fields, header/footers, custom style sets, etc.
There's an add image option in pdf.js when I use the (modern browser) demo.
Edit: added an image, saved the PDF and it does indeed include the image I added.
LibreOffice Draw is an excellent and very useful PDF editor. Just make very sure you have all the same fonts!