i would like to know if it would be possoble to convert a old save file (GDT V1.4.3) to the new steam version, because i had alot of things on my other save file and i would like to have it in the newer version of GDT.
Thanks for your help.
No, this is not possible. The save files of Game Dev Tycoon (the Greeneheart Game Store version) got saved in one file, while the Steam saves are different and there are more files. It would be almost impossible to convert the old version to the Steam version. Sorry! 
As @LineLiar were saying… Yes, it is not possible to transfer a non-steam savefile into the steam files. Sorry. :[