Microsoft has confirmed that Microsoft Word for Windows can save PDF files to a hidden local folder with a random file name when users try to store them in SharePoint Online.
According to a Microsoft known issues support page, the problem affects Microsoft 365 for Windows version 2609, build 16.0.20430.x, and Word shows no error when it happens.
Microsoft says the bug only triggers in one workflow: using Save or Save As, choosing the PDF file type, and selecting a SharePoint location. The issue status is listed as "Workaround", which means no fix is available yet.
Where Word 2609 Puts the Missing PDFs
Instead of landing in the chosen SharePoint folder, the PDF is written to C:\Users [username]\AppData\Local\Microsoft\Windows\INetCache\Content.MSO. The file name is randomized as well. One affected user reported files named 1f10f000 and 458d72b7 instead of the original document name, so searching for the document title will not find them.
Word behaves as though the save succeeded. Colleagues who open the SharePoint folder later simply find nothing there.
The original user report did not involve SharePoint at all. It came from someone saving a PDF of a document stored on a network drive, running Version 2609 Build 16.0.20430.20032.
Anyone who saves PDFs to a location other than a local drive should treat the bug as relevant. There is a privacy side too, since documents meant for a secured SharePoint site end up as copies in an unprotected local cache folder.
How to Recover Lost PDFs and Avoid the Word Bug
To check whether a PC is affected, open File, then Account in Word, and look under About Word. Version 2609 with a build number starting with 20430 is in the affected group. PDFs that already went missing can be recovered from the cache folder:
Open File Explorer and click in the address bar.
Paste %LOCALAPPDATA%\Microsoft\Windows\INetCache\Content.MSO and press Enter.
Sort the folder by Date modified so recent files appear at the top.
Open the randomly named PDFs created around the time of the save, rename the correct ones, and move them to their intended location.
Delete leftover copies of confidential documents from the cache folder.
Recovery should not wait. INetCache is a temporary folder, and Windows or cleanup tools can empty it at any time.
Microsoft's official workaround is to save to an alternative location or to use File, Export, Create PDF/XPS Document, which produces the same PDF output without hitting the bug.
Saving the PDF to the local PC first and uploading it to SharePoint afterwards also works. Printing to Microsoft Print to PDF still functions normally, though printed PDFs typically lose clickable links, bookmarks, and accessibility tags.
Affected users report that rolling back to version 2608 build 20326.20072 resolves the problem, but a rollback requires a command line tool and pausing Office updates. Administrators can instead check which devices run 16.0.20430.x builds and point users who export PDFs to SharePoint toward the Export option.
The Word bug follows a separate update that deactivated Office 2016 and Office 2019 licenses in September. Microsoft has not said when a fix for version 2609 will ship.