I have a lot of PDF files that were edited by Adobe Acrobat for which pdfinfo reports a warning:

Syntax Error: Marked object is wrong type (boolean)

I believe I have located the problem: This warning is emitted when the Marked key in the MarkInfo entry in the document catalog has a value of "false".  That *should* be an allowed value, but pdfinfo emits the warning due to the following code in Catalog.cc (within getMarkInfo):

    if (catDict.isDict()) {
      Object markInfoDict = catDict.dictLookup("MarkInfo");
      if (markInfoDict.isDict()) {
        Object value = markInfoDict.dictLookup("Marked");
        if (value.isBool() && value.getBool())
          markInfo |= markInfoMarked;
        else if (!value.isNull())
          error(errSyntaxError, -1, "Marked object is wrong type ({0:s})", value.getTypeName());


There is no problem when the Marked key has a value of true, or if it is omitted altogether.

This issue appears in poppler 0.66, and as far back as poppler 0.39.