Thanks for the response Jesse.
Our site is an ecommerce one, and every product page is supported with a pdf. This is expected from our customers and it basically is the product page in a PDF format with tweaks. We have 10,000s of these and for speed, we store files such as pdfs and images locally in a subdomain.
For content delivery network purposes, I heard it was better to keep pdfs, images separate as well? We haven't got a CDN but it's something we will look into next year.
Do you recommend scrapping the subdomain in such an instance and hosting them all in the main domain in a folder? Would that impact on page load and speed?
Also is it possible to redirect individual subdomain URLs to a main domain one?