PDFs are one type of document often found on websites and many marketers wonder how these can play into search engine optimization (SEO).  When thinking about PDFs from an SEO perspective, there are few things to take into consideration.

First, search engines do index PDF files, and believe it or not, they can rank fairly well.

Links from PDFs to a website can actually be valuable. PDFs typically have fewer links (if any at all) and therefore, all SEO weight that could be passed from the PDF is transferred through those few links, if any are present.  If the PDF is located on a site other than your own, and if there links pointing to your website from within the content of the PDF, these can be beneficial for your website, especially if keyword rich anchor text is used. (This is only the case if the other site does not restrict access to their PDFs.)

Also, keep in mind that if the PDF is shared among other websites, just like any other web page, they have the potential to be seen as duplicate content. When the search engines find duplicated content on more than one domain, the preferred one to display in the search results is often up to the search engines’ discretion.

That said, even though PDFs can rank well, it is generally not recommended to use PDF as targets for search.  They have little to no navigation back to the website and as a result, they end up being dead ends for users as well as for search engines. They also tend to have a high bounce rate in the results pages because they involve downloading a file, which some searchers don’t want to do.

To target the content within a PDF for SEO purposes, it is best to create new pages of content on the actual website to target the main keyword of the PDF and include a link to download the PDF version. Often, the content will not be exactly the same as the PDF, so it will be less likely that one version will be filtered out by the search engines as a result of duplicate content.  This also allows the visitor to download the PDF, if desired. As a best practice from a usability perspective, it is usually a good idea to restrict access to these files, so long as there is a page that supports the keyword targeted content. This can be done easily by making them all accessible under one directory such as /pdf/.

Browse around your website (especially the News, Press or Events sections) to see if you have any PDFs that could be utilized as a way to build out additional pages on your website. There could be more opportunities than you imagined to expand your keyword reach.

Implementing redirects is of the utmost importance when it comes to SEO. Whether running a Microsoft IIS or an Apache server, webmasters need the ability to implement redirects for old and alternate versions of your URLs. For example, if users are able to access the www version and non-www version of a website, these versions of the URLs are considered separate entities by the search engines and negative issues could arise.

For instance, both versions of your website could essentially be “diluting” your PageRank. If you have several inbound links to the www version of the site and several more pointing to the non-www version of the site, the importance Google assigns to you based on your inbound links is adversely affected. PageRank (represented by the little green icon on the Google toolbar) is the importance Google assigns to a page based on an automatic calculation that factors in the link structure of the web and many other variables.  The green icon on the toolbar shows a scale of 1-10, with a PageRank of 10 being the highest. The magic numbers of 8-10 are usually reserved for the “big guns” such as Google, Yahoo and Amazon.com.

A page that is linked to by many pages with a high PageRank receives a high rank itself. If there are no or very few links to a web page there is no support for that page. Although it has been argued that there is very little correlation between PageRank and your actual rankings in Google, it is still an effective way to gauge how important Google thinks your website is. Once the correct redirects are implemented, the search engines should transfer link popularity from the old URL to the new one so that the search engine rankings are not affected. The same behavior occurs when additional domains are set to point to the main domain through a 301 redirect.

The search engine friendly way to redirect URLs is to use what is know as a 301 (Moved Permanently) redirect. Multiple domains (www vs. non-www or separate domains publishing the exact content) can be deemed to be duplicate content by the search engines and your website could get penalized with automatic “de-indexing” or rank reduction in the search engines. Avoiding this is crucial to your website’s SEO success and survival.

The keyword density tool is a standard part of any search engine optimization tool arsenal but how important are the results of the tool for determining how well a page is optimized? What role does keyword density play in the search engine algorithms?

First, as far as we know, keyword density has never been the formula used by search engines to calculate keyword relevance for a page. Unfortunately, we don’t know what the true formula is (it’s a secret and Google won’t tell).

Most believe that it is actually based on term weight and that would probably be a better way to evaluate keyword use on a web page. However, one of the main components for calculating term weights is the total number of times the keyword is used on the internet. We have no way of knowing what that number is because even if we could crawl the whole internet and find all the pages and all the words, we still wouldn’t know if our crawl was the same as Google’s or Yahoo’s or any other search engine. This is why we can’t create a tool to more sharply evaluate keyword use on a page using term weight – we don’t have access to all the data. (And it may also explain part of the reason why you see different results across search engines – they have different indexes).

However, there are some things we do know:

The number of times that the key phrase (or parts of it) appears on the page carries some weight. We know this because we have seen rankings change after keywords are added to pages. We have also observed sites undergo “penalties” for stuffing keywords into meta tags, alt attribute tags or in fine print at the bottom of the page – commonly referred to as “keyword stuffing”. Too many unnaturally placed keywords may trigger a spam filter and cause rankings to go down. This appears to be algorithmic so we have to assume that counting the keywords on the page has some place in the algorithm, however small.

The total amount of page content carries some weight. Pages with more content tend to rank better (all other things considered).

Overall keyword theme relevance carries some weight – search engines evaluate the content based on factors like proximity of the keywords to each other, ordering on the page, position in the overall body content, positioning in important places on the page, as well as the thematic relationship between the key phrase and other words on the page. In some cases, synonyms of the key phrase can even count toward keyword relevance. So, the algorithm is far more complex than a simple keyword density calculation, but keywords undoubtedly do feature in the calculation.

Finally, we know that if search engines cannot properly interpret the code on the page, they cannot “read” the content properly. This could result in parts of the code being included in the text indexing for the page possibly resulting in lowered overall keyword relevance for the page. Search engines might even have trouble seeing the keywords on the page which could affect any keyword weighting for relevance. While it is true that they likely attempt to filter out this kind of noise in the indexes, we do not recommend leaving it to the robots – it’s best to control what they see whenever possible.

So, we use keyword density analysis tools as a quick way to look at the content on websites the way that a spider might see it. If the keyword density is too high, it can be a signal that the page may trigger a spam filter. If the keyword density analyzer doesn’t find the keyword at all or the density is very low, it can indicate that the page is not appropriately targeted. Because the keyword density tool is basically a simple spider, if it cannot properly “read” the content, it could indicate problems with the coding on the site.

That said, if the content on the page is properly focused on the keyword theme of the page and the keyword appears in all of the important places, title tag, description tag, headline, a couple of times in the main text content (ideally in the first and last sentences), the text is probably fine even if you don’t get up to the “optimal” keyword density. Furthermore, if your key phrase is very long (more than 3 words), using it 4% of the time on the page would be very unwieldy so you may not even want to use the keyword that many times. Content should always be written for people first, with the keyword density tool just used as a kind of reality check to make sure that it’s also going to be okay for spiders. A real “optimized” page will have content that is useful for visitors and will attract quality inbound links.