If you get a word processor document from a Windows user, the chances are good that it's set in one of Microsoft's proprietary TTF fonts. If you've only got free fonts on your machine, then it's unlikely to render correctly.
Since we've already got high-quality free versions of Times, Courier and Helvetica (donated by URW for Ghostscript, originally), it would be helpful to have a set of fonts that were compatible with Times New Roman, Courier New and Arial -- using the same metrics as the MS fonts, but the glyph images from the URW fonts. (Where glyphs aren't present, they could be taken from one of the other freely-available fonts.)
There are already compatible fonts based on the Bitstream Vera family, but since the glyphs need to be significantly deformed to make them fit the MS metrics, they're ugly on screen and unusable for print media. Using the URW fonts as a basis should result in significantly better rendering.