duo·reader (Dual PDF Reader)

duo·reader is an installation-free web reader designed solely for "reading while referencing" long PDFs. Read one side. View the other. Your reading position stays put.

You can open distant pages of the same file independently in left and right panes. Scrolling and zooming work one side at a time. Synchronized scrolling is off by default. We've designed it so synchronized scrolling doesn't pull the main text away from you. Splitting isn't buried in a menu—it's right there in the toolbar.

Here's how we envision it being used:

Contracts: Read Article 7's liability clause while keeping the definition section's "Confidential Information" alongside
Specifications: Read the main requirements while viewing diagrams and tables 15 pages ahead
Manuals: Follow procedures while confirming notes and exceptions on the side
Pre-Acrobat work: Compare distant pages to decide deletion candidates. Leave the actual deletion to Acrobat's Organize Pages
Instead of the work Acrobat's Window → New Window does—arranging two windows side by side—do it all within a single browser window.

No account required. PDFs don't go to the server; they stay in your browser. We don't include annotations, forms, signatures, or sharing. It's not an editing suite.

English UI is the default, and you can switch to Japanese.

https://duo-reader.com/