TripleDes using MD5 hash question

I'm working on a process to decrypt data that is sent from a vendor application using triple des encryption.  I'm not sure if the vendor is using any type of hash on their end.   If I use an MD5 hash on the key, does that change the orignal key?  Would the keys be the same If the vendor encrypts without using an MD5 hash and I decrypt using an MD5 hash?  The same key should be used by both applications.
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