UniDocVLM: Enhancing Visual Reasoning and Document Understanding for VLM via Reinforcement Learning

Abstract

Document question answering over scanned pages requires two coupled abilities: (i) canonicalizing complex layouts into a faithful textual structure, and (ii) selecting and reasoning over query-relevant evidence from that structure. Most existing pipelines decouple OCR from retrieval-augmented reasoning and optimize OCR for global reconstruction, which often misaligns with evidence needs and causes brittle grounding in multi-page settings. We propose UniDocVLM, an end-to-end framework that unifies OCR and visual RAG within a single vision-language model: the model first generates a structured parse of retrieved pages, then activates question-relevant evidence from the parse to support grounded reasoning and answering. To train UniDocVLM under heterogeneous supervision, we introduce a unified JR-GRPO reinforcement learning recipe with lightweight, verifiable rewards, including format, layout-aware OCR, evidence-consistency, and answer-correctness signals, and route them to the corresponding parts of the output to improve credit assignment and reduce interference. Experiments on multi-page document QA benchmarks show that UniDocVLM yields more reliable evidence grounding and improves downstream accuracy under complex layouts.