TIKA-4756

[tballison]

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[Copilot]

Pull request overview

This PR (TIKA-4756) improves PDF signature detection by distinguishing presence of AcroForm signature fields from presence of an actual applied signature, enabling correct reporting for PDFs that include unsigned /FT /Sig fields.

Changes:

• Add new PDF metadata flag pdf:hasSignatureFields to indicate /FT /Sig fields exist even if unsigned.
• Update PDFParser.extractSignatures() to set PDF.HAS_SIGNATURE_FIELDS based on PDDocument.getSignatureFields() and only set TikaCoreProperties.HAS_SIGNATURE when a non-null PDSignature is present.
• Extend PDFParserTest with a new regression test for an unsigned signature field scenario and tighten expectations for the existing AcroForm signature-related test.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
tika-parsers/.../PDFParserTest.java	Adds assertions and a new test to verify unsigned signature fields are detected without reporting hasSignature.
tika-parsers/.../PDFParser.java	Updates signature extraction to report signature-field presence separately from actual signature values.
tika-core/src/main/java/org/apache/tika/metadata/PDF.java	Introduces PDF.HAS_SIGNATURE_FIELDS metadata property.

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