Safari 5.1 can't display certain PDF files

Dear Apple fans.

Perhaps someone can put me on the right track since I am nearly loosing my sanity. Last month I downloaded my E-statement from a bank without any problems. These statements require an Adobe Viewer plugin to display in the Safari window. PreView just will not do it. This month for some reason it no longer works.

All that I can think of that changed is that I routinely downloaded various Apple software updates. And I can't tell exactly what was updated but I think to remember that my Mac OS was previously 10.6.7 while it is now 10.6.8. I am not sure if Safari was also from a previous version. The current installed version is 5.1.

Testing so far:

1. I removed ALL versions of Adobe including the famous plugins in HD/Library/Internet Plug-Ins as well as the same in User/Library/...
2. I reinstalled Adobe 9.4 which I had previously installed and which worked.
3. Checked presdence of new plugin --> OK, but no success when trying to view the statement.
4. I tried the same approach with Adobe X. Prior to that removing all files from the previous Adobe 9 installation but also here no success.
5. However, when dragging Adobe formatted files into the Safari window they are displayed OK.

Any suggestions perhaps from people who design the web pages for banks what other plugin might be required? The message I get is always the same: "Missing Plug-In" and when I click on "details" I am directed to the Adobe X download site.

Your comments are much appreciated.