HI,
DroidScript can read files, but these "books" have their own internal structure within the files.
For example FB2 (frequently ZIP'd) uses xml to contain footnotes, images, text formatting, Unicode, etc.
AFAIK there's nothing built into DS. There may be plugins (or you could write them, or have them written).
Another possibility is just to send an intent to another app (ereader) to open the book
(then the user reads the book in that app).