Can't change file association in Outlook Expr

Hello,

I'm running XP Media Center SP3.

I recently installed a trial version of Adobe Acrobat 9 Pro (9.3.3). I changed my file association for pdf files to Acrobat Pro.

The trial has run out; I may or may not buy. Meanwhile, I have changed the pdf file association in XP back to Adobe Reader. Now when I double-click a pdf file from Explorer, the file opens with Adobe Reader.

My problem is with pdf attachments to email in Outlook Express. When I receive such an email, and double-click the attachment, Adobe Acrobat Pro opens -- and fails, because the trial period is expired. I receive many pdf attachments, and this is a terrible nuisance!

I suppose that if I uninstall Acrobat Pro, the problem might go away. But surely there's a way to fix the file association. I would have assumed that all XP file associations simply grandfathered into Outlook Express. Apparently that's not true!

Can you help me fix this?

Thanks in advance,

Paul in WI