lines besides screen after conversion

[mareli]

Hi, my first post here, so if I make mistakes, please have mercy.

My problem is this:
I converted from several different format files (LIT, EPUB, MOBI) to RTF using Calibre.

I formatted those RTF files with word (2003), putting margins, centering and including a little indentation for the first line.

Them I imported them on Calibre (1.0) and converted them in EPUB (conversione default values).
When I opened them with my ereader (SONY PRS650) I had to enlarge the character and sometimes the line continues besides the screen.
It's the first time something like this happens to me.

Am I doing something wrong? Is there a way to resolve it?
Thanks for any help