Writer2Epub is an extension useful to create EPUB files from various filetypes that can be opened with LibreOffice Writer (DOC, RTF, etc), meaning the extension easily creates various files to EPUB using LibreOffice Writer.
The advantage of this plugin is the generating of high-quality EPUBs, fixing, in the same time, formatting errors and various issues, creating EPUBs compatible with the most common eReader programs/platforms.
If you are looking for a program to convert one or more files with arbitrary format to ePub format, keeping the original formatting rules and layout, then you should give it a try.
The plugin is actionable via three top-left icons: Writer2Epub (create the EPUB file), Metadata (edit metadata values, as well as adding cover images) and Preferences (fonts, file split, image quality, etc).
Installing Writer2Epub extension
Download the Writer2Epub extension from here. After download you just need to double-click on the oxt file. LibreOffice will open and it will install Writer2Epub. You can also install Writer2Epub by opening LibreOffice and selecting, menu Tools > Extension Manager...
For a detailed desciption on using the Writer2Epub Extension you can refer to the official wiki page.