Re-write a manual and sell it?

[Ben]

I've working on a documentation/reference/manual for a program, and I've just found a pretty similar document online which is good but wasn't written in English first and could badly do with basically being re-written. 

What's the legal/moral issues of this? 

This guide I found is distributed free under a 'GNU Free Documentation License' which states: "[Modified] Copies may also be sold commercially, but if produced in larger quantities (greater than 100) then the original document or source code must be made available to the work's recipient." Can someone explain what I can, can't do with this document and what I can do with my re-written/new version?

I'd planned on selling the document I was producing (albeit for a small amount), but I'd like to use section sof the guide I found but these will be re-written but would probably have the same screenshots however. So it's not exactly the original, but I don't want to step on any copyright toes.

Any advice? 

[Chris H]

http://www.gnu.org/licenses/

You can do what you will with it as long as you release it under the same licence and have the original available or distributed if over 100 units flogged, and give the original author credit.

[JasonD]

The GNU FDL does not quite state what you say it does

"If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy," [or say where you can get the Transparent copy.]

For those not reading the license, the Transparent copy is the one you can edit.

You are allowed, encouraged even, to sell GNU FDL licensed documentation, but do remember that anyone else who obtains a copy is entitled to do the same. Don't plan on retiring on any profits. Of course if you were to right a new manual from scratch then you are free to license it anyway you like, but that would be daft if half the work has already been done.

[Notorious MCSE]

Dont rewrite a manual.

Write a user guide to the software instead. 

[civ]

If you users are buying a manual, 99% of them are unlikely to know or care what that licence means