The Portable Document Format (PDF) developed by Adobe can be made accessible, but it very much depends on how the original document is designed. If it is a poster created in a publishing application, scanned or saved from a Word document and locked down for copyright reasons then saved as PDF, it is liable to act in the same way as a picture. This means the text cannot be read by a screen reader or adapted for easier reading. It is appreciated that the concept of the PDF is to ensure that printed or saved versions of a document remain as the author intends, but there are ways to help the reader who uses assistive technologies or requires different formats of the text and graphics.
Usability is the science of making web sites easy to use, enhancing the user experience and allowing the user to find information efficiently. It is not the same as accessibility but for practical purposes we have included within our accessibility guideli