Você pode tentar o calibre .
calibre is a free and open source e-book library management application developed by users of e-books for users of e-books.
Source Conversão do formato Ebook
What formats does calibre support conversion to/from?
calibre supports the conversion of many input formats to many output formats. It can convert every input format in the following list, to every output format.
Input Formats: CBZ, CBR, CBC, CHM, DJVU, DOCX, EPUB, FB2, HTML, HTMLZ, LIT, LRF, MOBI, ODT, PDF, PRC, PDB, PML, RB, RTF, SNB, TCR, TXT, TXTZ
Output Formats: AZW3, EPUB, FB2, OEB, LIT, LRF, MOBI, HTMLZ, PDB, PML, RB, PDF, RTF, SNB, TCR, TXT, TXTZ
Note
PRC is a generic format, calibre supports PRC files with TextRead and MOBIBook headers. PDB is also a generic format. calibre supports eReader, Plucker, PML and zTxt PDB files. DJVU support is only for converting DJVU files that contain embedded text. These are typically generated by OCR software. MOBI books can be of two types Mobi6 and KF8. calibre fully supports both. MOBI files often have .azw or .azw3 file extensions. DOCX files from Microsoft Word 2007 and newer are supported.