A free app for Android, by OnlineConverting.

This is a useful app for converting documents to ebooks. It supports many formats, and the conversion process is very easy to use. You can convert almost any document (e.g., PDF) to an e-book format.

In addition to PDF, the app can also convert to other formats, such as ePub, AZW3, LRF, TCR, SNB, RB, PML, PDB, OEB, MOBI, LIT, EPUB, and FB2. It can also convert images to ebooks.

It has an intuitive user interface, and the file selection is easy to use. You can choose multiple files to convert. The output format is determined by the file type.