What advantage PDFs?

What search engine advantage is there in displaying your thoughts in PDF format, rather than in plain old HTML? I'm sure I mentioned this only a few weeks ago, but I've seen another example of this on a website today.

On the site today, the home page is PR1 and the internal pages that or lower. Except for the information stored as a PDF document - that's the only PR2 page on the site.

It's not a site built, intended or used for search engine traffic. There's no link building scheme to help the search engine rating - the page rank is just what it's got from the few sites it's linked through, including my portfolio.

I noticed on my own site a few weeks ago that a couple of PDF documents that are only linked to from 1 page have a higher PR than the page linking to them. This goes against convetional wisdom as to how page rank is inherited - it's supposed to diminish as it is inherited, not increase.

So why is this and why could it be happening? Well, the first and easiest answer would be that Google hasn't fully updated and that the higher level pages have dropped, but not the PDFs. I know with my own site this hasn't happened. Maybe there's an increase coming, but it's only showing on the PDFs. But that would be too hopeful that both sites are going to increase in page rank...

So what else? Well, I can only assume that page rank works on multiple levels. You get the main level of a page rank, which is what inheritance is based on. Then you get marked down (and maybe up???) depending on other page factors.

What could these be and why? Well, with a PDF it's not full of links to other sites - or even your own. It's an end product that someone can pickup, print out and read. It's not full of Google Adsense or affiliate adverts and they aren't created just to drive traffic to your site - because people arriving there may never actually visit your site.

Or maybe it's just as simple as you lose some of your page rank by linking out to other pages. Now, how many people does that make sweat!

Whatever the reason, and it will be easy to monitor the situation through a couple of page rank updates, it does seem that there is a page rank advantage to putting your materials into PDF format. But, what advantage does this actually give you? It's difficult to then put links into your site - people would have to cut & paste or even retype the required URLs and maybe find the page they are after on the site.

I suppose that's why there is a page rank difference - if you are supplying the information it is just to give that information to your visitors. There would be no great advantage for me to fill Compare Mortgage Rates with information in PDFs, because there's no guarantee that anyone reading the information is then going to visit my site to click on adverts etc.

I suppose in some markets it can work. I'm working with pure strike on their website. With them, golfers might be reading up about golf putters and if they read about the pure strike putter and saw the URL they probably would be interested.

So maybe reviews etc would be useful in PDF format, but not for affiliates. As an affiliate I could write up how brilliant a driver is, but then the reader is just going to go off to find the cheapest about, they aren't going to come to my site to by it.

There must be a few good ways of using this quirk. How, I haven't quite worked out. And that's probably the answer - move up the search listing results that are there for results, not because people can manipulate the traffic that arrives.