Google’s John Mueller recently discussed how Google processes PDFs for ranking purposes, how it indexes them for use in AI Mode and regular search, and why it is able to use links in PDFs the same as it does for regular HTML web pages.
PDFs Are Converted To HTML
Google’s Martin Splitt explained that Google uses a converter to transform PDFs into HTML, and then it indexes the HTML conversion, not the actual PDF. He also expressed uncertainty about whether images in PDFs do or do not get indexed. He appeared to lean toward the possibility that they do not get indexed and said that this state may change at some point in the future.
“And what we do is we are not using a PDF viewer. …What we are doing in Search is we have a component called a converter. And the converter component is part of what happens in indexing. It happens right after rendering and right before something potentially makes it into the index.
One of the things we do is we look at the format. We have converters for a bunch of different formats, such as rich text files, document files, Excel sheets, and Lotus Notes documents for some reason. But also one of them is a PDF converter. So we are taking that and producing an HTML version of it so that the processing in the rest of the pipeline pretty much only works with HTML.
That’s obviously excluding images and videos and yada yadayada—those go to slightly different pipelines—but the normal web pipeline pretty much uses HTML for everything.”
Later on he explained how Google handles images in PDFs:
“I think we might actually pick them up. I’m not sure how we would process them because the way that we normally process them is that we give the URLs of the image to the image search pipeline that then works with this.
Here we don’t really have a URL because it’s part of the PDF. So I think we understand there is an image, but I don’t think we can actually process it like a normal image for image search. But that might change or might have changed; that’s my current understanding of how that pipeline works.”
Links Work In PDF Files
Google also confirmed that links embedded within PDFs function like links because it’s the HTML version of the PDF that gets indexed, which includes the links which can be followed like normal links.
“So basically when Google sees a PDF file, it converts it into something that it has more practice with, kind of a web page. And I guess that’s also why things like links also work in PDF files.”
“Yep. Because we convert it into an HTML page and then the rest of our systems are like, “I know how to deal with an HTML page,” and they just do their stuff.
…So a lot of stuff can be embedded in a PDF. And when we convert it, we convert it to a representation in HTML that is as true as is possible to that original format. So we can see things like links, for instance, from PDFs.”
Google’s PDF Size Limits
Google’s Mueller acknowledged that they don’t know everything and that they’re trying to explain PDF indexing and ranking according to what they do know.
He asked about PDF file size limits.
“I realize some of these things maybe we just don’t know the details, so we’re kind of trying to extrapolate from what we do know. Do you know with regards to limits, like size limits, how that works with PDFs?”
Splitt answered that the file limit for PDFs is larger the way that video size limits are larger, but that he didn’t know the exact limit. He added that he believed that normal HTML limits apply once the PDF is converted, which is useful information.
“Probably fetching the PDF has a different limit than the web page limit, but probably there’s a limit for the web page kind of representation.
I’m not so sure where these limits are applied. I know that the HTML limits that we recently discussed on the podcast and in documentation as well come from the crawling component of the pipeline. So when we crawl them, as we have to crawl a PDF document and PDFs can be really large, I assume that we have a larger file limit, just the same as we do for videos and images. But I don’t know the specific limit for PDF files.”
Later on Splitt said that whatever the size limit is at today could change in the future if they detect that people are publishing larger PDFs.
PDFs Can Rank In Search And AI Mode
Martin Splitt also confirmed that PDFs can rank in AI Mode for the same reason it can rank in regular search. Google converts the files to HTML then indexes it like that.
But he also mentioned that not all PDFs can rank for the text because some PDFs are like images. He suggested that if you can highlight and copy the text from the PDF to a text file then Google will be able to convert the PDF to HTML for ranking purposes.
Splitt explained Google’s PDF rankings in response to the question of whether site publishers should create PDFs:
“Yeah, sure, if your content warrants it. Like if you have specific formatting requirements, or if you need this stuff to look really, really specific in print, or if you need interactive things like forms.
So if you are running a holiday lodge and you are publishing a form that makes it easier for you to process people who are registering to stay at your holiday lodge, then absolutely do this as a PDF if it helps you.
Obviously HTML is a really flexible format and I prefer that, but if you have a PDF for whatever reason, go for it. Restaurants oftentimes have the printers create the menus that they actually physically print on paper as a PDF as well, and you can just upload that to your website. It’s better than not having your menu on the website at all.
…indexing and ranking is pretty much the same as any other document.”
“So they can also appear in AI overviews, AI mode, all of those things.”
HTML Is Probably Better For SEO Than PDF
Later on in the podcast Mueller expressed that regular HTML is likely better for ranking purposes. That does not diminish the ranking power of PDFs, but there’s a pragmatic angle about making it easier for search engines to rank web documents.
He first expressed this idea in talking about Menus:
“I see it a bit pragmatically. If the option is have a menu as a PDF or don’t have a menu at all,then yes, I would prefer to have a menu. But if the option is menu as a PDF versus a normal web page, I kind of like normal web pages because it’s easier to interact with them.”
Then later on he referred to Martin’s comment about the indexability of PDFs:
…From an SEO point of view, if it’s indexable text—if you try that trick that Martin mentioned, selecting everything and putting it into a text editor—then we can use it for search. It’s not that from an SEO point of view it’s impossible.
Then further on he expressed the idea that if a site owner can do it in HTML then to do that:
…if you have something that you can put into HTML and it’s just the same as your PDFs, that makes everything a little bit easier.”
That last point about making it a little bit easier gets to the fundamental heart of what SEO is all about, which is making it easy for search engines to crawl and index website content.
Listen to the Search Off The Record Podcast here:
