Just stumbled across this on a Google search.
Adobe Labs have a pre-release of how to support Adobe Reader v8.1 ifilter on 64bit sharepoint.
I’ll admit that I haven’t tested this yet and it involves a 64bit ‘thunking’ layer. In the past I have seen some instructions on to use this technique to ‘hack’ together a custom 32bit ifilter handler onto a 64bit system.
The main significance of this is that currently the only cleanest way of supporting pdf indexing on sharepoint 64bit platforms is to use foxit pdf ifilter. However this is commercial software that is priced based on the number of CPU cores. (As at 25JAN2008 this was “License cost for each server with up to two CPU cores is $329.99. Each additional CPU core costs $129.99.”) Now with most production servers these days being dual quad core processors (ie 8 processing cores) This would be US$1109.93 for each production server. Congrats does go to foxit for seeing a large hole left in the market by Adobe being so slow to support the 64bit platform and providing a solution.
The other comment worth making is that the foxit 64bit ifilter may be coded natively in 64bit but I’m not sure of this. Whereas the Adobe solution is taking the existing 32bit ifilter in wrapping it into 64bit which does involve a processing cost overhead. If you had a large index with lots pdf documents then going for a native pdf ifilter could bring a significant performance difference.
Gavin's Sharepoint Blog 