lopdf vs pdfium in Rust — What I Learned Building a PDF App

All tests run on an 8-year-old MacBook Air. All results from shipping 7 Mac apps as a solo developer. No sponsored opinion. I built Hiyoko PDF Vault — a macOS PDF tool — in Rust. Choosing the right PDF library was the first real decision. lopdf or pdfium. Here's what I found. lopdf: pure Rust, no dependencies lopdf is pure Rust. No C bindings, no system libraries, no bundling headaches. What it does well: Merge, split, rotate pages Read and write PDF structure Metadata manipulation Bates numbering Works well for structural PDF operations What it struggles with: Rendering PDFs to images (not its job) Complex font handling Malformed PDFs — lopdf is strict; real-world PDFs often aren't For a tool that manipulates PDF structure without rendering — merge, split, encrypt, add watermarks, strip metadata — lopdf is the right choice. Pure Rust means easy cross-compilation and universal binaries with no extra work. pdfium: full rendering, C dependency pdfium is Google's PDF engine (from Chromium). The pdfium-render crate wraps it for Rust. What it does well: Accurate PDF rendering to images Handles malformed PDFs that lopdf rejects Text extraction from complex layouts Full PDF spec compliance What it requires: Bundling the pdfium binary with your app (~20MB) Architecture-specific binaries (x86_64 and aarch64 for universal binary) More complex build setup For a tool that needs to display PDFs or extract text from complex documents, pdfium is the right choice. You pay for it in bundle size and build complexity. What I actually use lopdf for structural operations: merge, split, encrypt, watermark, metadata, Bates numbering. Apple Vision Framework (via Tauri shell commands) for OCR — it's already on the user's Mac and handles Japanese text better than anything I could bundle. I avoided pdfium because the bundle size increase wasn't worth it for my use case. If I needed accurate rendering, that calculation would change. The honest recommendation Start with lopdf. It covers most PD