PDF File Handler is a separate and optional Office 365 Add-in that enables opening PDF files in PDFSF Cloud directly by clicking on file name in a document library. This enhances user experience, as otherwise users need to select the file and click on the custom action button to open the file.
In order to uninstall PDF File Handler:
Step 1. Open https://portal.office.com/myapps
Note: you need administrator permissions to access this page.
Step 2. Find PDF Share Forms application
Step 3. Click ... → choose Remove from tenant
Step 4. Confirm removal
Now PDF files in SharePoint libraries will use default application to open PDF upon clicking. In order to open PDF files in PDFSF Cloud viewer users need to select a file and choose Open PDF in Browser.