The ways a default appearance string (DA) departs from what ISO 32000-2 §12.7.4.3 requires; what was readable is still read.
[Flags]
public enum PdfDefaultAppearanceProblems
ISO 32000-2 §12.7.4.3 and Table 228; operators and their operands per §7.8.2 and Table 50.
kind:method, kind:property, kind:ctor. Press Esc to clear.FontOperatorMissingNo usable Tf operator: §12.7.4.3 requires one, with its font and size operands.MultipleTextMatricesMore than one Tm operator; §12.7.4.3 allows at most one. The last one is used.NoneThe string is well formed.OperandsInvalidAn operator had too few operands or operands of the wrong type, and was ignored; or too many, and only its last ones were used; or operands were left with no operator after them.OperatorNotAllowedAn operator not allowed within a text object (Table 50, Figure 9), one that would unbalance the appearance stream around it (q, Q, marked content), or an unknown keyword; it was ignored.SyntaxInvalidA token that cannot appear in content (a lone ), an unbalanced ], a malformed number) was skipped or repaired (§7.8.2).