Edit PDF in sharepoint online

Andrew Silcock It works just as you'd expect. SharePoint or OneDrive content PDF file opens in the browser routing by way of documentcloud.adobe.com. The free version only lets you add comments and highlight/markup. But if you sign-in on Adobe and you have a license then you get all tools like combining pdf files, managing pages, etc. (license is not cheap of course - you pay per user/month).

Have your O365 Admin install the App on your tenant and give it a whirl its free - but likely you are exposing any PDF you open to Adobe (which you'd be doing anyway if you signup for the digital signing option).

InBrowser Editing