Does anyone write plug-ins for Adobe Photoshop\CSxx? Need advice

Question

Adobe

The most important question is whether there is intelligible documentation \ examples \ getting started, etc.?
Adobe downloaded the CS5 SDK from the site, but the content is a little strange, for example, there is quite a lot of documentation in PDF, but if you open these docks, they are full of messages that this is outdated documentation and you need to use documentation in HTML (why then should these PDFs be included in the composition? SDK??)

Documentation in HTML with inconvenient navigation and lack of search, it also contained links to articles from 1999 (which talks about 5.xx versions of FS) and it is not clear why this is better than the "outdated" PDF (which are 2005-2007 years).

It is not very clear with plugins - there are several types of them and there are those for which it is written that the documentation / examples for them are available only by request, but where and to whom to write? the documentation does not mention such details. It is also not clear what kind of licenses there are, in Google I found mentions that Adobe closed access to the SDK and limited the development of plug-ins, changed licenses, but meanwhile you can download the SDK on the Adobe website (maybe the SDK is not complete? Or something else? )

It is also not clear what is with compatibility and whether plugins written for CS2 or CS3 will work under CS5, etc., I only met mentions that there are various kinds of problems if you write both under Win and under Mac or support 32-bit and 64-bit platforms.

In general, I will be glad to any advice / links to resources. While I'm picking the docks from Adobe and looking on Google, but the results are contradictory and not accurate, I haven't programmed for Adobe products before, maybe I'm looking in the wrong place?