Raindrop.io now supports PDF preview and highlighting on web, desktop, and mobile. A custom PDF rendering engine was developed due to browser limitations and the need for server-side rendering to enhance performance. Highlighting PDFs is simple and all highlights are stored with the document. However, users must save PDFs as bookmarks in Raindrop to highlight, as built-in browser viewers do not support highlighting. Users can find all saved PDFs in the “Documents” section of the app, allowing seamless integration with other saved content.
https://blog.raindrop.io/pdf-preview-and-highlighting-41391d06fe90