I'm promoting use of the FDL for textbooks and lecture notes at our university. It critically depends on section 3.
Why are you promoting use of FDL when you don't want your own work to be free? Or, at least for that work you don't want to be free, FDL makes no sense.
The specific question is: *If I publish my own work as a PDF under the FDL in the web, do I need to provide the LaTeX sources?*
As the copyright holder you can do whatever you want, since noone likely has standing to sue you. However, so doing makes the licence worthless, since the rights which it attempts to grant are not effectively granted that way.
- IF it applies, how many units are published when I put the file
online? One? As many as downloads? [1]
My understanding is, as many as downloads.
- IF more than 100, publishing the pdf without the tex violates the
FDL. Yet, since only the copyright holder could pursue the offence, and that's me, for all /practical/ matters I'd be fine?
You'd be fine, but you wouldn't be granting the rights the FDL is designed to grant, so why bother licencing the work under the FDL in the first place? Issuing contradictory licences isn't useful, and it degrades the "brand value" of those licences, if you see what I mean. People who see an FDL-covered document have and should have the expectation that it is effectively free within the meaning of FDL, and applying FDL to documents which are not reduces the confidence people place on such promises.
Clearly, I can't recommend to use a license and infringe it: What license would you recommend for those who like the FDL but are unwilling to reveal their LaTeX sources?
It depends on what is it you like about FDL. Perhaps a Creative Commons attribution, no-derives, would serve your purposes? No-derives since, hiding the source seems to be directed towards that aim, although I'm not sure why you don't want to expose your LaTeX, so can't say.
[1] If one publishes as often as there are downloads, the license would encourage taking content offline as soon as 99 are reached -- hardly the intention of a free license. Also, since this timed taking offline is a prohibitive effort, the FDL would discourage putting the document online: It was made for ~20 students, so handing print-outs would be FDL compliant. I don't believe the FDL wants to provide incentives to hide the text offline, either.
Well, the FDL primarily doesn't want to provide incentives to hide the source.
HTH --David.