Unfortunately, I haven't heard of many certifications that the industry respects. I think the MarketMotive program is a good one, but that's more for the training than the piece of paper, IMO.

It really depends on your goal. If it's for clients or your employer, get the certifications they value. It's all about perception, in that case. If it's for selling your services directly, I'm not sure I'd bother. The training can be good, but you still have to pound the pavement.

I'm Google AdWords certified, for example. It's a decent program, and some of my existing clients like that I have it, but when I first got it, it did little or nothing to bring in new clients. The training program itself is good, but you can do that without ever paying them a dime or taking the test.

Is there a specific aspect of SEO you're trying to learn?

If they duplicate your main content, I think the header-level canonical may be a good way to go. For the syndication scenario, it's tough, because then you're knocking those PDFs out of the rankings, potentially, in favor of someone else's content.

Honestly, I've seen very few people deal with canonicalization for PDFs, and even those cases were small or obvious (like a page with the exact same content being outranked by the duplicate PDF). It's kind of uncharted territory.

Oh, sorry - so these PDFs aren't duplicates with your own web/HTML content so much as duplicates with the same PDFs on other websites?

That's more like a syndication situation. It is possible that, if enough people post these PDFs, you could run into trouble, but I've never seen that. More likely, your versions just wouldn't rank. Theoretically, you could use the header-level canonical tag cross-domain, but I've honestly never seen that tested.

If you're talking about a handful of PDFs, they're a small percentage of your overall indexed content, and that content is unique, I wouldn't worry too much. If you're talking about 100s of PDFs on a 50-page website, then I'd control it. Unfortunately, at that point, you'd probably have to put the PDFs in a folder and outright block it. You'd remove the risk, but you'd stop ranking on those PDFs as well.

I think it's possible, but I've only seen it in cases that are a bit hard to disentangle. For example, I've seen a PDF outrank a duplicate piece of regular content when the regular content had other issues (including massive duplication with other, regular content). My gut feeling is that it's unusual.

If you're concerned about it, you can canonicalize PDFs with the header-level canonical directive. It's a bit more technically complex than the standard HTML canonical tag:

http://googlewebmastercentral.blogspot.com/2011/06/supporting-relcanonical-http-headers.html

I'm going to mark this as "Discussion", just in case anyone else has seen real-world examples.