I was editing pdf drafts from a publisher and just couldn't stand another minute of dealing with Acrobat. Found this, removed all vestiges of Adobe, and haven't looked back.
I've used Preview a lot, but it just isn't reliable (for me). Apple seems to muck around with the code every couple of versions and break things. Odd.
1) Defaulted to setting PDFExpert as my PDF viewer,
2) followed with a survey I could not close out,
3) required an account to begin.
I'm happy it works for you but I'm tired of the modern software that wants accounts, your data....
Readdle's apps, namely 'Documents', have always been my go-to on iOS for editing PDFs and transferring files[1].
But they went and added a useless VPN to Documents, then released a 're-design' which cuts functionality (and from the reviews is quite buggy). It's sad to see a quality app degrade as the developer adds bloat and new 'features'.
1: For example, Documents (which edits PDFs as well) has a built-in WebDav server that is super useful for getting files between an iPhone and a Linux machine over Wifi.
If the ipad versions of illustrator and photoshop have the features you need that's the only way you can avoid all the nagware. I only need to do the occasional edit to a logo or photo so the ipad pro versions are enough and I prefer the pen to a mouse. I've stopped using them on desktop and use https://smallpdf.com for editing and signing pdfs.