A free app for Android, by Real TechnoLab.

This is a very useful application for scanning and saving documents in PDF format. You can use it to scan multiple pages of books, multiple sheets of paper, and even multiple sheets of a notebook. You can save all of them in PDF format on your device. 

You can also use it to scan images and save them in PDF format. It can also be used to create PDFs from other types of files. It supports a wide range of formats, including JPG, JPEG, PNG, TIFF, GIF, BMP, TGA, XCF, PSD, XCF, and more. It also supports a wide range of paper types, including paper, notebook, journal, and more.