I'd like to use Windows Search for searching through multiple PDFs in one go, but I see that in the Indexing Options' Advanced Options screen, PDF files don't have a registered IFilter:
What is an IFilter, and where can I get the appropriate one?
IFilters allow Windows Search to search within file contents.
Here are three popular PDF IFilters. They are ordered by search performance according to this article:
After installing one, you should be able to search within PDF files in the same way that you can for other types of files.
An alternative way to search through PDFs is to use the search function of PDF-Viewer. It does not need indexing neither. This is my choice.