A search showed, maybe for Psd or for Pds Usually, you can look to see if they have 'your' extension before you do anything. I saw some that seemed to be for free. Also, who is the source company, maybe check their web site. Is/was your old program compatible with windows xp or for a mac? If this doesn't help, maybe you can provide more details and also post, instead, in "PC applications & utilities forum".
Good luck,
Eddie