I recently helped a VB6 developer who was deploying CR v8.5 reports.  His application reports could not export to PDF in some installations.  This is an old but still popular configuration, so I am posting what we learned because it might help someone else down the road (maybe even me).

The first thing we found was the specific DLLs that support PDF export.  We had to confirm that they were part his distribution:

ExportModeller.dll
Crtslv.dll
Crxf_pdf.dll
Mpr.dll
EFSADU.dll

But even if the files are distributed and installed you still have to make sure that they get registered correctly.  And they won’t register correctly if there is another file that the DLL depends on that is missing.

So here are instructions to determine if a DLL is registered:
http://social.msdn.microsoft.com/Forums/en-SG/netfxbcl/thread/206787e7-3a59-4b02-b2d6-eda0a50e1459
(look at the posts on 2/17 and 2/18 – probably the last posts in the thread)

Here is a free tool to show all registered DLLs
http://www.nirsoft.net/utils/registered_dll_view.html

Here is a tool to show all files that a DLL depends on, which might prevent it from registering:
http://www.dependencywalker.com/

And if you really are stuck you might want to talk to Randem Systems, they are mentioned in this post:

http://kenhamady.com/cru/archives/220

They know as much as anyone about the CR runtime and the files that are needed.