The effort of typing "adobe psd format specification" on any search engine is very low and it returns the page above.
Maybe OP just nerdsniped themselves and never thought of taking a moment and checking better online? Not sure.
My comment wasnt very focused. I didnt mean to say author missed a google result. Rather, TODAY psd spec is readily available. I don't think it was as easy to be found when author wrote that comment in 2008 or whatever.
NTFS, HFS, Microsoft Office formats, many cameras' RAW formats, etc. were reverse engineered with blood sweat and tears to allow interoperability and rescuing some information from them in dire situations for years now.
Paragon Software won't be able to give their NTFS source code to Linux Kernel if they got the docs from Microsoft. Microsoft have made Paragon disappear overnight.
Edit: Just found out that Paragon still updates and maintains the mainline driver in the Kernel. Huge props to them.
Addenda: The first snapshot of this particular webpage appears in Jan 15, 2011, titled July 2010 [0]. This particular incarnation of format is born in 1990, if we believe the Copyright lines in the beginning.
There's also a small CSS change comment from "25 Jun, 2009" in the beginning. So the page was present in 2009.
[0]: https://web.archive.org/web/20110115150245/https://www.adobe...