Edit PDF in sharepoint online

For my main client in medical communications, being able to edit PDFs directly from SharePoint is a Holy Grail that is proving very elusive. Two years after this topic was started and the situation is no better.

Does any 3rd party PDF editor work really well with SharePoint? A lot of them (e.g. Nitro Pro and Foxit) purport to work with SharePoint but their user interfaces are horrible and unworkable - esp. if you use a lot of Office 365 groups which use normal SharePoint document libraries. 

I really don't understand why the PDF developers can't implement a better interface to SharePoint. They've done the hard work with being able to open via WebDAV - just need better ways to bookmarking document libraries.  And certainly a better way to search for document libraries associated with Office 365 groups - and then bookmark. 

I've developed lots of software over the years and know how to access SharePoint (mainly from PowerShell but idea is the same). I'm pretty sure I could improve the Nitro Pro SharePoint interface in a few days.

But the biggest blocker here is Microsoft. Sure, you can "Open in Word" direct from the web browser, but where are the hooks to allow "Open in Nitro Pro" or "Open in Photoshop" because yes, graphic artists really struggle as well.

And synchronisation via OneDrive isn't very attractive as that means you're encouraging copies of documents to be stored on the laptop. Kind of defeats "data never leaves the data centre" approach. Plus you loose record locks and end up with version clashes. Neat - not!

Really, I'm very confused why this hasn't been solved yet. Would mean my client wasn't so reliant on network locations...