pdf files are not getting indexed

Hi,

I am using EPiserver 10 hosted in Azure cloud. I am using EPi find 12.5.0. I have three sites sharing same code base and different databases. Each site have Dev, Test, ACC and Prod. Interestingly, Two of the sites in all environments shows pdf indexing. One site shows pdfs in Prod environment, but shows "localhost" in links. Same sites ACC and Test environments does not shows pdfs. 

1. My question is why only two sites (Test and ACC) does not shows pdf.
2. Why same site in Prod environment shows "localhost" link to pdfs.

Thanks & Regards,

Sanket Mahimkar