@davidb22099501 The PAC (PDF Accessibility Checker) tool is much stricter than Adobe Acrobat's internal viewer, which is why Acrobat can open the file fine while PAC considers the structure "corrupted" and flags the specific error. The error message: "Pg entry of marked-content reference and of parent structure element is null." This error means the PDF's internal structure tree has an element (a tag) that doesn't properly reference a page number (Pg entry is null). This is a structural flaw that breaks the PDF/UA standard, making the file inaccessible to screen readers, even though it may look correct visually.
You can try to fix the PDF by opening your PDF in Acrobat Pro. Go to the Tools menu on the right, select Accessibility, and then click on Full Check. When the options box appears, make sure everything is checked and that it’s set to check All pages, then click Start Checking. Once the check runs, it will give you a results panel. Look for the main error it found (it might be called "Tagged content failed" instead of the long error name). Right-click on that problem and choose Fix. This is Acrobat’s best attempt to automatically rebuild the broken parts of the document's hidden structure, which usually clears up the "null page entry" issue that PAC is complaining about. If that automatic fix doesn't work, you'll need to manually check the Tags panel (look for it in the Navigation Panes under View), and use the Reading Order tool to find and correctly tag any content that may have been missed or broken during the file's creation. Once you save the repaired PDF, PAC should see a clean, structural file!
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