I recall Matt Cutts, in one of his videos (https://www.youtube.com/watch?v=z07IfCtYbLw), addressing product descriptions (Scraped from the manufacturer) with E-Commerce sites, especially those sites that are selling products that a hundred, or even a thousand other retailers are selling. He said that you would be ahead of your competition if you took the time to rewrite those descriptions, so they are original and not duplicate content . It is not necessary to refresh or rewrite them every couple of months. Just having a unique description that no one else has for that product will put you ahead of everyone else selling that product.

It would be a good idea to try and get your customers to write reviews on your products and post them on your product pages. This is unique, original content that is fresh. Amazon is a good example of doing this.

With my company, which has several major domain sites and a mother-ship root domain, we've had this ongoing discuss of moving all our subdomains to subfolders. Our concern is the pain of the transition in losing valuable traffic until the subfolders gain value and traffic. So we have the following subdomains:

boatcovers.iboats.com

boatpropellers.iboats.com

biminitops.iboats.com

forums.iboats.com

And all our other products are listed under iboats.com. Is there a painless way of making the switch to move our subdomains into subfolders and not get killed on traffic?

There are a couple of things you can do that will help your product pages rank better over your pdf pages. You can do a canonical from the pdf to the product page it is referencing, giving your product page the ranking value. You can incorporate your pdf into text (html) on your product page, giving your product page additional, relevant content, thus boasting ranking.