Highlights vs Mozilla PDF.js

Highlights is a PDF reader for research that turns PDF annotations into notes, available on iPhone, iPad, and Mac. Its free plan supports reading and annotating PDFs, merging annotations, editing PDF metadata, and Handoff. Notes can be exported as Markdown, TextBundle, HTML, WebArchive, or PDF, or sent directly to supported apps including Evernote, DEVONthink, Ulysses, Bear, and Keep It. For scientific articles, Highlights can find DOIs and retrieve metadata; it can link to a PDF on the device if the citation has already been read. Built-in multilingual OCR extracts text from PDFs without searchable text, with processing done on device. Smart Copy outputs copied images as PNG, tables as CSV, and citations as BibTeX. PDFs can be stored on device, in iCloud Drive, Dropbox, or another sync service, while annotations use standard PDF annotations. On macOS it integrates with Bookends and Papers. The free plan is available alongside Pro at $4.99 a month or $29.99 a year. The maker describes the app as intended for students and researchers.

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.