PDF Accessibility Checker 3 (PAC 3)^[25] by Access For All is a freeware utility for Windows that checks PDF files for PDF/UA conformance. The program implements the Matterhorn Protocol checks. When you open a PDF file in PAC 3, the program runs its checks and shows a summary of the results. Since there is no interactive checking, the program can only warn about some of the failure conditions that require human checking.

Figure 2. PAC 3 PDF/UA checker