try installing a different anti virus. They are often the cause of slow loading on PDF files. This is usually associated with slow opening of Office documents as both are well known sources of malware they get the full monty in scanning which can be incredibly slow.

Thanks for the suggestion.

I tried disabling all antivirus applications on the workstation, the problem still occurs.

You ue the term workstation. Is this a corporate environment with remote data stores and perhaps RDP

It's an enterprise environment. RPD is disabled. Server type is IMAP and problem exists even after the the file has been fetched. eg: the file has been opened once, so is saved in local folders. I think the problem is probably not network related or I would see this more often. Occurrence is >1% of installs.

Try deleting the Action for pdf files in Tools/Options/Attachments/Incoming, then restart TB, open a pdf attachment, and select the opening app, i.e. Reader. Don't select from the list of apps, but Browse to the correct exe file.

Thanks for your suggestion.

The problem continues to occur after deleting the action, restarting and setting the application manually.

Look at the temp folder on the affected machines. Often slowness is a byproduct of years of abandoned temp files.

Anti virus scanning also occurs in the temp folder, and clutter can have large effects on speed of anti virus.

Whilst I would bot recommend a permanent exclusion you might want to try without scanning in that folder or at all in the diagnostic process.

Are the profiles stored on the server? Check the size of the folders the mail resided in on disk (right click properties). Clear the cache in options just to be sure it is not one of those issues which a cache falls over itself, they do not always make things faster.

Thank you again for your further suggestions

The machine I am trying to address this on now is a new install, there is no issue with clutter. The problem continues when the antivirus is disabled. Yes the profile is stored on the server, though data is downloaded locally before being opened/executed. It is IMAP. The profile is ~2.6GB After clearing the cache from all history the problem continues.

I tested disconnecting the machine from the network and the problem continues.

Opening other document formats works fine in all circumstances, only PDF experiences issues.

The issue exists for all users accounts on the machine, even newly created accounts.