Squid

The app doesn’t require registration and it allows you to import PDF documents and use editing tools just like on any other file. You can use a pen to take notes or write naturally using your finger. It has features for managing multiple paper types and sizes, use select, move and resize tools on documents. Notes can be exported to PDF, PNG or JPEG files for printing, sharing or archiving.
 
Moreover, the application lets you create shortcuts to create new notes and organize notes in multiple categories. In addition, you can cut, paste, copy items between notes or import and resize images inside documents. Squid also lets you use premium background, like math, music, sports or engineering.