Nowadays, a lot of information is shared using pdfs. A lot of content on the web is also available as pdfs. To open a downloaded pdf file, the user has to break out of the web sandbox and use a local application to view it. Over the last years, browsers like Safari and Chrome come with PDF viewers build into the browser. Chrome has done a lot of work to make the pdf renderer secure, but it still runs outside of the web sandbox.
pdf.js tries to solve this by rendering the pdf in the web sandbox. This is also serves as a prove of what's the web platform is capable to do and what pieces are missing.
Student at the ETH Zurich