The opinion here, at “What’s On My PC”, the best ebook converter is Calibre. This software application is actually a fullscale e-book manager that allows you to do nearly everything and it takes things a step beyond normal ebook software. It’s also completely free and open source and great for both casual users and computer experts.
Calibre has been in development since October 31, 2006, is completely free (open source). Calibre is available for download on the following platforms: Windows (32 and 64 bit), macOS, Linux, and as a portable app.
How popular is Calibre? Active installs: 2,795,543 (those that have started calibre at least once in the last 60 days).
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: AZW, AZW3, AZW4, CBZ, CBR, CBC, CHM, DJVU, DOCX, EPUB, FB2, FBZ, HTML, HTMLZ, LIT, LRF, MOBI, ODT, PDF, PRC, PDB, PML, RB, RTF, SNB, TCR, TXT, TXTZ
Output Formats: AZW3, EPUB, DOCX, FB2, HTMLZ, OEB, LIT, LRF, MOBI, PDB, PMLZ, RB, PDF, RTF, SNB, TCR, TXT, TXTZ, ZIP
Source: Calibre – ebook management