There is already a reader for txt files. That document program for Doors, there is also a online converter from txt to calc-programs.

yeah, it's a seperate download. You can get it here

There's also FlashBook. It lets you convert text files into apps, with varying levels of compression, a table of contents, custom fonts, etc.

many people don't use doors here though.  It causes my calc to crash all the time.

You might have to report the errors to Kerm, though, as DCS is the only shell that is still maintained anymore.

But yeah there are still e-readers for calcs. I think Notefolio and another one (Textview I think). Also before converting books, make sure you don't violate author rights.