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How to set, reset, remove and recover the password of excel files 
Click on the office button, select prepare, and then choose encrypt document 
Enter a password in the password box and then press ok. 
Re-enter the previous password to confirm and then press ok. 
Save the password and the ms excel 2007 document.
( note: as microsoft advises, you must not forget the password or you will not be able to get into the document. If forget, you have to turn to third-party software like excel password rescuer for help.