This private project was started long time ago (since july, 2015).
Today, I decide to public beta version of kunvertor.com or chuyendoipdf.com
In this project, I used:
+ symfony2, mysql as web app
+ nodejs + redis as real-time server
+ gearman as job queue server
+ apache pdfbox to extract text from pdf (http://pdfbox.apache.org/index.html)
I will spend more time to write more detail about how to implement this stuff.
Now, breath deep and go to sleep 😉