FILE CASE - employee has typed a letter in my name and then signed himself on behalf of me without consent

Hi All, An employee from my organization has typed a letter in my name and then signed himself on behalf of me though not taking any kind of consent from me.
PLEASE HELP.

Hi M.Banerjee,
This action is a disciplinary case, go to your HR and ask them to help you.

Dear M Banerjee,
This is more than indiscipline. It is plain forgery. I recommend you conducting the domestic enquiry and terminating the employee. However, do not terminate the employee without conducting the domestic enquiry.
Why the letter was issued? What was the purpose? Has the employee left the job already? Ask the employee to submit the original letter to your office. If he does not do it, then you may file a police complaint.
Thanks,
Dinesh V Divekar