Documents must be accessible as well.
Make sure they can be accessed properly and that the images and language are correctly set. Ensure your document heading structure is logical and doesn't skip heading levels. Most of the instructions about writing accessible content also apply to documents.
Web pages are generally more accessible than files. When adding a file, consider whether it would be better to present this information as a page rather than a file.
Word and Adobe Acrobat Pro both offer a tool for checking accessibility in a document. These tools cannot check for all things related to accessibility but they are a good start.
If you use Windows, you can also use PAC PDF Accessibility Checker to test for document accessibility.