PDF editing on Mobile

http://www.toughdev.com/content/2015/02/comparison-of-popular-pdf-libraries-on-ios-and-android/
http://androiddeveloperspot.blogspot.sg/2013/05/android-pdf-reader-open-source-code.html
http://howto.wikispaces.umb.edu/PDF+Annotation+with+Android



http://www.radaeepdf.com/
https://www.pdftron.com/pdfnet/mobile/android_pdf_library.html
http://www.qoppa.com/android/pdfsdk/

https://github.com/gearit/RadaeePDF-Cordova


https://github.com/Ink/ThatPDF
http://mupdf.com/