Getting Finder to open the right version

Question

I recently updated my copy of Adobe Acrobat Reader from 5.0.5 to 5.1. But the new version doesn't work.
How do I get Finder to open the old 5.0.5 version when I double-click on a PDF file (without deleting the new 5.1 version)?
Gary

Answer 1

"The app starts with a splash screen that indicates it is loading plugins. Then it simply quits. The only remnant is a zero-length file in the trash."
Reader 5.1 shouldn't simply quit, provided that you're running OS 9.1 minimally. Its OS requirements specify this, so if you're running an older version of the Mac OS, then a problem might be expected.  If the installer were a corrupted download, you should have tried downloading and installing it again.
"And it's a GOOD thing that I didn't throw the old version away first. If I had, I'd have no way to open PDFs at all."
My suggestion to delete the older installed version was not a recommendation for you to "throw away" anything.  One should always keep older program installers stored on another medium, for future use.  Didn't you save the Reader 5.0.5 installer after downloading it?  If not, the download link at Adobe's web site can be found here.  Years ago, I saved so many third-party, freeware downloads for pre-OS X software to multiple CDs.  Corporate acquisitions (such as AMD's acquisition of ATI) often cause a decline in web-based support, in spite of promises to the contrary.  AMD dropped the popular (pre-OS X) ATI Universal Installer 4.2 - I assume - because it was considered obsolete.  One should always backup downloads for safe keeping, because there's no gurantee that you'll be able to obtain them later.  VersionTracker was always a good source for older Mac downloads, until it was absorbed by CNet.  That's when many of the files became unavailable.