inspired by https://github.com/mozilla/pdf.js and https://github.com/AlloyTeam/AlloyFinger
查看PDF的工具/The tool which read the PDF
打开viewer.html，传进去参数url = 1.pdf,例如viewer.html?url=1.pdf
open then viewer.html in browser, add the param "url", such as viewer.html?url=1.pdf