Drag and drop a document to annotate it.

Works with .pdf, .doc, .docx, .xls, .xlsx, .epub and .csv files.
.doc and .docx are converted to .pdf.
.xls and .xlsx are converted to .csv.

You can also annotate PDFs inside Google Drive by authorizing Hypothes within your Google account. Hypothes.is PDF Annotator will be listed under the "Open with" option for PDF files upon authorization. (Uninstall).

Scanned PDFs will be OCR’d
(please ensure text is horizontal).

The OCR service uses Tesseract, an open source library.
You may have better results using a professional tool (tutorial). The annotation functionality is enabled by Hypothes.is.
The code for this site is open source.

This is a personal project to explore different ideas and is maintained by Dan Whaley. I’d be delighted to hear any feedback at @dwhly.

The intention is to keep the site up and running, but no guarantee around the preservation of documents is made.
As an aside, annotations against PDFs with your Hypothes account, are discoverable on that PDF regardless of its location (Background). As long as you have the original PDF somewhere, you'll always be able to see your annotations on it with Hypothes.