I followed the guide "go to My documents, open the file LDW, open Plant tycoon folder.." But all the files in that folder are: "plant tycoon0.ldw, plant tycoon21.ldw, plant tycoon1.ldw, ldwlog.txt". Please help, can't open any of these files at all. Anyone knows how to save the game in this case?

Copy plant tycoon1.ldw and plant tycoon21.ldw to a safe place on your computer. You don't need to open them.

The game is saved automatically every 10 minutes. The procedure that you are referring to is for backing up the game files so that you can restore them if you have a problem with the game due to a crash or similar event. The guide also says not to try to open those files, since that will damage them if the program you open them with changes them in any way.

okie, Thanks. It means after I hv saved the 2 files plant tycoon1.ldw and plant tycoon21.ldw to another folder, I can use the virtual seed tray safely, right?

Yes. That way, if you do encounter a problem, you can recover your games and not lose all your hard work.