Usually the cause of documents being slow to open in Word is when the attached template is missing – especially when the template is located on a network. Turns out with Word 2010 there can be another reason.
We had a client where some documents were taking between 25 and 30 seconds to open, but only for some users. Word displayed Validating. Press Esc to Cancel in the status bar, but pressing Escape didn’t help.
A bit of research about what the validation process does led me to this article http://blogs.technet.com/b/office2010/archive/2009/12/16/office-2010-file-validation.aspx.
I then found that disabling the validation process by setting the following registry value made the documents open instantly.
Interestingly the offending documents appear in the list contained in the HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Word\Security\FileValidation\FailedFiles key, so there is something up with them, but we won’t go into that.
Now the other point the article made was that the process only runs on untrusted documents. This turned out to be the key. I re-enabled validation, and added the path to where the attached template was located as a trusted location, and voila, the document opened quickly.
In the end the problem turned out to be a group of users who weren’t getting their Workgroup Template path set correctly, so therefore the network templates were not being trusted.