The way I used to make documents readable on Sony, using Word, was to copy and paste into Word (if in another format); select all, then justify; select all again if necessary, then change the font size to between 16 to 20 pts, depending on the font and your preference.
On menu: file - properties, in the property box name the file as whatever you want to show up on the reader, same for author etc; click OK.
Then save as an rtf file.
If you want something more sophisticated, make a Word template, as I've done. Measure the reader screen: roughly 3.5x5inches or 9x12.3cm, then set up the page in that size and set the margins and paragraph indents/spaces as desired. Set the font size to one you prefer (N.B. it looks much larger in Word than it does on the reader so you may need to experiment a few times and reset the template). Then save as a template (in the save as drop down box). Name something like "ereader format".
Then anytime you want to save a file for the reader just open the template and paste it in. Save as rtf.
Hope that makes sense.