PDF backends

PdfConfig.backend selects PdfBackend::Native (default) or PdfBackend::Pdfium. Backend choice is explicit: never silently return native output when Pdfium was requested.

Native backend

• The native engine is xberg_native_pdf and supports the full Xberg PDF pipeline: text and structure extraction, page rendering/OCR fallback, tables, annotations, images, attachments, and richer metadata.
• config.force_ocr forces the whole document; config.force_ocr_pages selects pages. Otherwise, pages without usable native text can enter the OCR stage inside PdfExtractor; OCR is not a second PDF extractor in the registry.
• PdfRenderSession in pdf/render.rs opens document bytes once and exposes page count and page rendering. Use it for repeated page renders instead of reopening the same document for each page. It is a Rust primitive and need not be exposed by every binding.

Pdfium backend

• Pdfium requires the pdf-pdfium Cargo feature. Selecting it without that feature must return an actionable error.
• Runtime dynamic loading honors PDFIUM_DYNAMIC_LIB_PATH as a directory containing the platform library. Build-time static and dynamic link variables are not interchangeable with runtime discovery.
• Pdfium binding is process-global and operations are serialized by the engine lock. Preserve that invariant when changing concurrency.
• The Pdfium implementation intentionally has a narrower capability surface: text, page count, and Info-dictionary metadata. It warns about omitted native capabilities rather than pretending parity.

Verification

Test backend selection separately from document semantics. A missing Pdfium runtime is infrastructure failure unless the job promises to provision it; when XBERG_REQUIRE_PDFIUM is set, skipping because the library or fixture is absent is a failure. Use corpus fixtures through the test-corpus skill and include Pdfium artifacts in benchmark aggregation when the adapter is enabled.