Flash?
That's quaint. All the cool kids are using pdf.js.
http://mozilla.github.io/pdf.js/web/viewer.html
On a site that's related to security matters and secrecy, given its prior record, doing stuff in Flash seems foolhardy
Wikileaks' Flash-powered PDF reader has sprung a vulnerability or two. The whistle-blowing website uses an open source Flash library called FlexPaper to display PDF files. Unfortunately various coding errors left FlexPaper open to cross site scripting and content spoofing. Developers behind the open source web based document …
As someone who works under the hood on PDF, I am sorry to inform you that pdf.js is shit. It handles the easy stuff OK, but there's an awful lot it doesn't handle correctly, or at all. Customers finding documents are rendered incorrectly in pdf.js and filing bug reports with us make it the bane of our lives.