From the about page:
Sharing and reviewing documents and presentations with others can be quite a pain. Crocodoc was built to change that, alleviating the need to email attachments back and forth, print and pass around hard copies, or install expensive collaboration software.
Crocodoc takes your PDFs, Word documents, and PowerPoint presentations, and lets you view and mark them up online. Documents can be shared with others, who can collaboratively highlight or strikeout text, add notes and comments, and make revisions. All files are stored securely on our servers, and can be password protected and encrypted for maximum security.
Crocodoc is based in San Francisco, CA.