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Converted ResourceFinder to ParserCallbacks so we can better detect the name that precedes various operators and use the operators to sort the names into resource types. This enables us to be smarter about detecting unreferenced resources in pages and also sets the stage for reconciling differences in /DR across documents.
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If not found in the field hierarchy, /Q and /DA are supposed to be looked up in the document-level form dictionary. /DR is supposed to only come from the document dictionary.
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This results in a performance penalty of 1% to 2% when replaceObject and swapObjects are never called and a somewhat larger penalty if they are called, but it's worth it to avoid very confusing behavior as discussed in depth in qpdf#507.
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There are lots of things with /Kids that are not pages. Repair the pages tree, then do a reliable check.