Well, depending on the OS and the commands in the .bat file, yes, it can harm your PC. A .bat file is a batch file, which is a file that holds a "batch" of commands. Almost like a script file but not as powerful. That said, it could hold a command like "del c:". You might want to double check if anything was deleted. You can open the file with notepad.exe since .bat files are in clear text.

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You might want to make sure that you can see all extensions in your email.