EHPDFHeadlessAppearanceError

The typed error raised by HPDFHeadlessAppearance for invalid options, malformed fonts, embedding permissions, invalid Unicode, missing glyphs, budgets, and unsupported text layout

Failure returns THPDFHeadlessAppearanceFailure; the exception message describes the exact condition

Cancellation uses the existing EHPDFOperationCancelled contract, while document field policies and security checks use EHPDFHeadlessDocumentError