Can PDF, Flash and MS Office documents have PageRank?
The question today is – does Google assign PageRank to non-HTML files such as PDF files, Word documents or Flash files? Here is the definite answer.
Contents
Introduction
PageRank is just one of the many algorithms that Google uses to rank web pages. However, it is definitely the most well known and, due to the Google Toolbar, one of the most visible.
PageRank originally applied only to web pages, and not other types of files such as Adobe PDF files or Microsoft Office documents. However, Google has indexed these types of files for a long time now, so it would make perfect sense for Google to try and treat these in a similar way to web pages.
A caveat regarding the robots exclusion protocol
As with any test, it is important to ensure that there are no external factors which could affect the results. In this particular case, the Robots Exclusion Protocol is one such factor.
This quote from Matt Cutts sums the issue up nicely:
“a page that is blocked by robots.txt can still accrue PageRank. In the old days, ebay.com blocked Google in robots.txt, but we still wanted to be able to return ebay.com for the query [ebay], so uncrawled urls can accumulate PageRank and be shown in our search results.”
This means that we have to be careful to ensure that any files which we check are not blocked by robots.txt – rather than the non-HTML file itself having PageRank, it could simply be that the URL is blocked by robots.txt. To be sure that Google really does assign PageRank to a particular type of file we have to ensure that it is not blocked by robots.txt.
Note: Although the quote above applies to robots.txt, we have also checked that the files do not have an X-Robots-Tag HTTP header.
What types of files does Google index?
If you go to Google’s Advanced Search page, Google provides options to search for files in a number of formats:
Google also has a list of supported file types on its file types FAQ page.
Note: We are not going to do an exhaustive list of different file types in this post, but the above list is a good place to start. Also note that we have not looked at images or videos, which have their own Google search verticals.
How we looked for non-HTML files to test
To find non-HTML files which might have PageRank as quickly as possible we used Google’s filetype: operator. We used this operator on its own, rather than combining it with a search query. For example, to search for PDF files we used the query [filetype:pdf].
Note that Google’s filetype: operator isn’t perfect – for example, it will return normal web pages ending with the same extension (for example, here’s a web page with a URL ending with .doc). Therefore, we also have to check each URL to make sure it’s actually the type of file we are looking for.
Results
Note that we are not interested in how high or low the PageRank scores are – what we are looking for here is simply whether they have any PageRank or not.
Adobe Portable Document Format (.pdf)
http://www.deetonline.org/brochure.pdf
(PageRank 4)
Microsoft Word documents (.doc)
http://www.wvnn.com/privacy_policy.doc
(PageRank 4)
Flash files (.swf)
http://www.uclalive.org/ucla_live_event_news.swf
(PageRank 6)
Excel spreadsheets (.xls)
http://www.post.ch/pm_dp_jahresplan.xls
(PageRank 3)
Plain text files (.txt)
http://www.rarlab.com/themes_new.txt
(PageRank 5)
We also wanted to check whether Google gives PageRank to file types which aren’t on the list, so we checked a few additional file types:
Microsoft Word 2007 documents (.docx)
http://www.antor.com/EUROPEAN_TRADE_AND_CONSUMER_SHOWS_CALENDAR_2009.docx
(PageRank 4)
"Comma-separated values" files (.csv)
(a format used for spreadsheets and storing data)
http://www.edeltutiyama.com/hayami2008.csv
(PageRank 1)
Conclusion
Our research has shown that Google PageRank does not just apply to web pages – it also applies to a range of other documents.
Please note that proving that PageRank applies to the file types examined above only shows that it applies to these particular file types – to be absolutely certain that PageRank applies to a particular file type not listed above, you’d have to check it in the same way.