PDF is not accessible enough for people with disabilities, limiting their ability to access information effectively and undermining their independence and privacy.
Understandability means users can read the content, predict what the interface will do, and get help when they make mistakes. 67% of users abandon forms when they encounter complexity.
Operability means every user can navigate and interact with your interface, regardless of the device or assistive technology they use. Keyboard access is where it starts.
Perceivability means presenting information in ways users can actually perceive. If your content is invisible to assistive technology, it doesn't exist for the people who need it most.
The four WCAG principles boil down to a simple question. Can every user perceive, operate, understand, and rely on your interface, regardless of how they access it?