A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi jonmcad,
Unfortunately, there is no such an app that can open and edit PDF files on Office portal for now.
In my opinion, you can use Word or Excel to create your forms which will save to your OneDrive automatically. And you can share this form to others with a link or put it on the SharePoint site. In this way there won't be any downloads or uploads to your PCs or Local severs.
Meanwhile, you can try Microsoft Forms which is also an online app, you will find it in your portal > Explore all your apps. Here is an article about its usage.
Regards,
Alex Chen