Resources not indexed

Hi all. A Client has said that some PDFs in resources are not being indexed by Google and can I make them indexable. All I can see is an Options -Indexes entry that I always add to .htaccess to stop people browsing the directory but this shouldn’t discourage search engines… or does it?

Any ideas what’s going on? Not sure why they need the PDFs to be indexable anyway but they do.

Are these PDFs linked on websites? Or only existing inside the resources folder without reference?

Yes, linked on the website. Their marketing lady says indexing would be good for SEO - lots of keywords !