This is exactly the sort of thing Mythicsoft search products do. To restrict the search to only PDF file types use the 'File name' field and enter something like:
If you want to restrict the search to multiple types you can separate the types using a semi-colon, e.g. to restrict the search to PDF, TXT and DOC files:
If you know part of the file name you can restrict the search using a colon, e.g. to restrict the search to PDF files with the word 'tortoise' use:
The same trick works with groups of files, e.g. to restrict the search to PDF, TXT, and DOC files with the word 'help' you could use:
Note: Some of the functionality described is only available with FileLocator Pro version 6.5 and higher.