Adobe's ubiquitous Portable Document Format, or PDF, has been very popular for sharing documents on the web for a very long time. While PDFs are not the best way to present information on the web - if at all possible you should put the content in an HTML web page - they are useful as an additional, alternative content format that people can download for offline reading. When posting PDFs to the web, we can follow some best practises so that they are more easily crawled by search engines, and are accessible.

Make your PDF accessible

The best way to ensure that the search engines can properly index your PDFs is to make them accessible. You can set up the original source document for accessibility, and those settings will generally carry over when converting to PDF.

If you have a document already in PDF, advanced PDF editor software such as Acrobat Pro / Acrobat DC have tools to help with editing the document to make it accessible.

Make sure that text is actually text, and not an image.

Search engines can’t read the text that is within images. If you do have an existing PDF that has text in an image, advanced PDF editors usually allow you to detect text in images using optical character recognition (OCR) and convert it to readable text. This will also make your PDF more accessible for those using screen reader software.

Add headings and document structure

When creating documents, we want to try to avoid big “walls” of text. Breaking down a document into sections with headings can help make a document easier to read and scan through. 

Within your word processor, use the Paragraph styles tool to apply structured headers to your document. Break down subsections with proper subheadings. Some examples of paragraph styles are: Title, Subtitle, Heading 1, Heading 2, etc..

Use bulleted lists where possible to concisely break down information into easily digestible bits.

Create accessible hyperlinks

If you have links within your PDF, it is important to make them as accessible as possible.

• Embed the link within text - Highlight the text you want to make into a hyperlink, and then use the hyperlink tool to add the link. Do not just paste a full URL within your document.
• Make sure the hyperlink text is descriptive of the PDF content

Color and contrast

• Ensure a strong color contrast between foreground and background on every document
• Never use color alone to show emphasis
• For charts or graphics, do not use color alone to separate information

Use alternative text descriptions for non-text elements

Use alternative text descriptions for images, charts and other embeds within your document.

Use descriptive file names

• Match the document filename with the document title
• Avoid punctuation or special characters in filename
• Use lowercase characters, and dashes instead of underscores or spaces.

For best results, use descriptive names that outline who created the asset, a product SKU, and/or an important subject keyword.

Link to PDFs within your website

Including links to your PDFs will give Google the signs it needs to recognize that these are pieces of content you want to have indexed and ranked.

Here are some tips for linking to PDFs:

• Optimize the link text to match the document title
• Avoid links like “Click here to download”- these do nothing to describe the document being linked to
• As a courtesy to your readers, indicate the document file type and size of the document
  • Note that printing the file size can usually be automated within your content management system.

Example (this article as a PDF):

Link to your website within PDFs

By linking back to your own web pages within a PDF, you can increase the likelihood that a search engine will view the content as an important part of your site.

Another great benefit that comes with using PDFs is that external sites are more likely to link back to them, due to their value as a permanent resource. If you include links within the document to important pages on your site, you can end up gaining authority (and rankings) for more than just the PDF.

Using PDF document properties

Search engines will index from the PDFs document properties metadata, which will allow us to set information like the title and a description.

The Title in a PDF ‘Document Properties’ section will be used by search engines in the same way as an HTML title tag. Similarly, the description will often show in the preview for the document in search results.

PDFs are typically best suited to ranking for specific, long-tail queries. By their nature, the documents hone in on one area of investigation – the title and description should reflect that. Optimizing a PDF for a broad, conversion-focused term is unlikely to be successful.

If you are the author of the original document, it is usually best to set the document properties in the originating application (such as Microsoft Word) before conversion to PDF.

If the document is already in PDF, you can use a PDF editor such as Adobe Acrobat (Pro or DC) to set the document properties.

Optimize for the mobile PDF experience

• Keep file size to a minimum – the smaller the better. Try to keep under 5 Mb.
• Downscale and compress images when converting to PDF.
  • JPEG compression (play with the compression level to get the right balance between file size and image quality)
  • downscale image resolution to 150 DPI or less.

Track performance

The objectives, from an SEO perspective, of adding a PDF to a website will be rather different to the addition of a product page, for example. That means that the measurement of its success will require a different mindset, too.

You can consider the download of a PDF from an organic search visitor to be a micro-conversion. This can be added to your analytics package as a goal, so you can see how many people entered the site via organic search and then downloaded the document.

You can get much more granular with this, to assess the path the user took within the site to land on the PDF, or which other marketing channels they interacted with before making this micro-conversion.

Resources:

• Creating Accessible PDFs - AccessibleU
• Defining PDF Accessibility - WebAIM
• Create accessible Office documents - Microsoft
• Accessibility Checker in Microsoft Office - Microsoft
• View or change the properties for an Office file - Microsoft
• Create and verify PDF accessibility (Acrobat Pro)
• PDF properties and metadata - Adobe