i have a .stp file but i can not open with any software. help me please!
Neudipr is probably right.
The problem with the file is with the header information. Two screenshots are below. One shows "normal" information typically found in a step file. The other shows the header for this step file.
Your file is either corrupted, or encrypted, but I can't think of any reason why someone, or some program would only encrypt the header.