Hi PhyrePhox,
I may be wrong but it looks as if your source LIT file is poor. It looks as if it's been created from a plain text file in MSWord which has not had its "hard line breaks" removed before conversion to LIT. My advice would be to try to clean up the source rather than editing the EPUB.
This is the approach I would take.
- Extract the HTML from the LIT by switching on the Debug option during the Calibre conversion of LIT to EPUB:-
[Convert] - [Debug] and specify a directory to receive the Debug files.
- Once the conversion is finished ignore the EPUB it created but go to the Debug directory you specified and look in the Input subdir. The extracted source HTML will be in there.
- You can then use your editor-of-choice to tidy up the source before re-importing to Calibre.
If you need more help I would be happy to take a look at your LIT file and give more specific help based on what I see.