For some reason the 64-bit versions of Windows has a problem indexing PDF files. Windows Search uses IFilter to help it index files, and the PDF IFilter for 64-bit Windows is missing. (This probably applies to 64-bit Vista and 64-bit XP as well).
To detect whether a computer has the IFilter installed or not open Indexing Options from Control Panel:
Find the PDF extension on File Types tab:
As shown above PDF Filter Description says “Registered IFilter Is Not Found“
To fix this problem download and install:
When everything is installed your filter description for pdf extensions should say “PDF Filter” instead of “Registered IFilter Is Not Found” in Indexing Advanced Options:
Before being able to search PDF-files the Index has to be rebuild. This is done by clicking Rebuild i Indexing Advanced Options:
Please note: Rebuilding index can take a long time if your disks contains large amount of data.