How do they know 'Where you left off'?

You’d be surprised how Office 2013 knows ‘Where you left off’.

One of the nice little features in Office 2013 is the ‘Welcome Back .. Pick up where you left off’ tag that appears when you re-open a document. image from How do they know

Click on that tag and you’ll move to the last place you were in the document. Very nice, though you could always use Shift + F5 in earlier versions of Office to do the same thing.

Most people would have thought this useful information would be stored in the document (the .docx file). After all it’s an XML file so it can contain all sorts of detail. You’d think that the document position, time accessed and the user ID would be saved there.

But no … it’s not. Microsoft has chosen to save it in the Registry instead!

Jason Hale has figured out that the ‘Welcome back’ details are stored at \HKCU\Software\Microsoft\Office\<version number>\Word\Reading Locations
in the registry. For Microsoft 365 the version number is 16.0

The document path and name are saved with the saved date/time and two numbers representing a position in the document.

The second number appears to be a location you have viewed (scrolled to) in a document; not the last edited or cursor location.

Looking through that registry location on a few working machines it seems to save details of documents, including PDF’s, opened in Word or via Outlook and saved in a temporary cache. Both locally stored and network shares are listed.

Potential privacy breach

For all the talk by Microsoft about privacy and security, this is a curious and glaring gap. Presumably, saving in the Registry was done for speed or perhaps merely to avoid a debate with the Office document format team about adding to the Open Office XML Schema (never underestimate the difficulties of intra-Microsoft communication and bureaucracy).

Saving these details in the registry means there’s an easily overlooked privacy breach. ‘Reading Locations’ contain both the path to and the document name. Not much on their own but useful information for any intruder.

What’s worse, these ‘Reading Location’ details are kept for the last 50 documents read by the Word user. That’s far more than the usual Most Recently Used (MRU) list that’s around 25 documents.