When searching the web we occasionally see PDFs and other non-HTMLs pop up in Google top 10. An example, well-known to every SEO, is Google's SEO Starter Guide.
Here are some more cases in point:
The DOC example was found by accident – there are very few high-ranking Word documents on the web. We looked for PowerPoint presentation and Excel spreadsheets samples, but couldn't find any - it appears they are not that common.
Anyway, top rankings for competitive keywords is definitely the case of PDFs. So here are some tips on optimizing your PDFs for search results.
Tip 1. Understand the general principle
The main reason why PDF documents are sometimes ranked above the HTML pages is that Google believes they provide a more relevant result, i.e. "they better serve the user". What factors are taken into account? Google voices only (1) user's behavior and (2) content relevancy. Since we can't influence the first component, let's focus on the second.
Tip 2. Do keyword research
Similar to optimizing regular web pages, brainstorm key phrases you want your PDF to rank for (jump here to learn how to do keyword research). Perhaps you'll need to alter the text accordingly. Pay special attention to optimizing the titles.
Tip 3. Make sure the text in your PDF is indexed
Google bot can easily read and index the text, not images, in your PDF. The rule of thumb is that if you can copy and paste the text from a PDF document into a standard text document, Google should be able to index that text.
What about scanned documents online, which are PDFs but are actually images, not texts?
Google uses the Optical Character Recognition (OCR) technology to convert them into words. Still, it's better to avoid images with texts (which scanned documents are) and not complicate the indexation task for Google.
To make sure your PDF is indexed trouble-free, also check out your PDF is not protected from indexation by X-Robots-Tag.
Tip 4. Think reader
Improve formatting and design of your PDF document – make reading it a pleasant experience. Apart from showing respect to your readers, you'll also make your PDF more appealing for linking. People don't tend to link to PDFs (partly because following a link and being stuck to wait for a PDF download can be a weird experience), so you should increase the chances of getting more backlinks.
Tip 5. Build links
Similar to HTMLs, PDFs should be supported off page as well.
As you can see, there's not much PDF-specific to do in terms of optimizing PDFs for search. What really increases the chances of your PDF ranking high is the value of the content you provide.