Mozilla PDF.js vs Universal Viewer

Mozilla PDF.js is a free, web standards-based platform for parsing and rendering PDF files. Developers can use its display API to render documents and retrieve information, or adapt the viewer layer for a custom interface. That viewer is used in Firefox and project browser extensions. PDF.js renders annotations and supports adding a subset of annotation types, and it supports form filling; OCR is not provided. The project targets HTML5-compliant browsers and includes a legacy build for older browsers, although PDF feature support varies by browser and version. Prebuilt builds are available, with hosted copies listed through jsDelivr, cdnjs, and unpkg. Developers can clone and build it locally, but some browsers require a local web server instead of opening PDFs through file URLs. Cross-origin requests are blocked by default, so CORS or a server proxy may be needed. For large documents, rendering only visible pages can reduce memory use. PDF.js is licensed under Apache 2.0.

Universal Viewer is a Windows desktop application for opening a wide range of file formats in one viewer. It handles images, multimedia, Word and Excel files, PDF, RTF, internet formats, text, and formats supported by Total Commander Lister plugins. Image support includes over 40 graphics formats and RAW images from 400+ cameras; its multimedia player supports over 170 formats without external codecs. In the Pro version, Word and Excel files including DOCX and XLSX open without MS Office, and a PDF plugin works without Adobe or Foxit Reader. Pro also adds complex RTF and RAW image support, an image panel with a Convert to feature, and highlighted text search. Text mode handles files of unlimited size, including those over 4 GB, with encodings such as Unicode and UTF-8. Windows Explorer context-menu integration provides a way to open files in the viewer. The free edition’s multimedia support depends on the Windows Media Player engine. Listed system requirements include Windows XP, Vista, 7, 8, 10, and 11. The Pro version has a 15-day trial; paid access starts at $26.