Why not use Word or Pages for the interior file?
Microsoft Word and Apple’s Pages are word processors. They were never designed to produce printed books. While there are excellent books (see resources below) that will show you how to format your Word file for upload to a digital printer, the best results are obtained by using a dedicated typesetting program like InDesign.
InDesign is a page layout program. It does things like kerning, tracking, and hyphenation that make a printed page look its best. Improper kerning and poor hyphenation show up as rivers of white space that trickle down a page, and portions of the text can appear stretched or crowded.
If you’re using graphics, either as illustrations or as decorative elements, it is difficult to position them accurately in Word and sometimes they may turn up somewhere different than where you intended. InDesign allows graphics and text boxes to be securely positioned where you want them.
If you’re using color graphics, Word may turn them into RGB images. Then when you output a press-ready pdf, they will be output as CMYK images. Better to start with properly prepared CMYK images that need no conversion.
Then there’s ligatures, those little flourishes on letters that join them into a single glyph. Some letters look awkward together, like fi or tt. InDesign merges the two letters into a single glyph that looks much better.
InDesign uses typesetting fonts—fonts designed for print. Word uses whatever fonts came with a particular computer system, fonts designed for reading on a monitor. Often a computer font will print too light. A premium typesetting font is optimized for ink on paper.
While readers may not understand why they don’t like the look of a page, they will know when it isn’t quite right. To get a professional product, you should use professional tools.
The images on the left are from an article posted by Joel Friedlander on his blog, The Book Designer. The complete article is linked below.