>   But which PDF should it be?
>
>   PDF letter for U.S.?
>   PDF A4 for the rest of us?
>   PDF for Kindle?
>   Kindle DX?

no matter which one you choose,
someone will be unhappy with it...

some of these devices do _not_
let you zoom in or zoom out, so
the .pdf has to be right-sized
from the get-go, or it's a no-go.

so you have to let the user specify;
see how feedbooks.com does it...

of course, there is the alternative
of giving 'em a tool that lets _them_
generate the output .pdf according to
the dimensions that they've specified,
which can entail more than pagesize.

including things like block-paragraph
vs. indented, curly quotes vs. straight,
choice of font, choice of font-size,
choice of leading, background color,
and any number of other variables...

or, you know, you can try to put _all_
of the options in your web-converter.

-bowerbird