Edit PDF in sharepoint online

I'm late to this discussion and very new to SharePoint. I'm in the consideration phase of migrating our cloud file server to SharePoint. Staff are used to accessing docs, xlsx, pdf, etc via a drive mapping in Windows Explorer.  So, SharePoint is going to be a culture shock and will need lots of training.  On just the issue of files:

We modify PDFs regularly as our staff will store an invoice "to be approved" in a particular folder.  They add a stamp with comment notes documenting the proper Accounting codes/accts and comments on the expense.  Their manager reviews invoices in the folder and will add a rubber stamp marking it as approved. The manager then moves the PDF into a "to be paid" folder for our accountant to go though.

From my brief Googling and experimentation, OneDrive seems to be the solution to this PDF-edit topic.  Staff can use the browser and would only be able to view PDFs, not edit.  However, if I sync the Sharepoint site, the site shows up in my File Explorer.  From there, I can double-click and open PDFs locally on the desktop with Adobe or we use Foxit PDF Pro.  When I save, it saves and syncs.  I can cut and paste the file in Explorer to move it between the folders.  

Am I right about this?  Am I missing something?