There are organizations which offer fake experience certificates and individuals who can give fake degree certificate. But a 3rd person submitting your documents as his, is not possible, that too in the same organization.
Only way it can happen is, he takes your documents, scan and Photoshop it. But then, question would arise as to how did he get your documents and how you came to know about this. Without assistance from an insider in your organization or the college where you studied, this is not possible. If I were an HR and get a complaint of this sort, I will look into the genuineness of your claim. If I am the police officer investigating this, I will also look into the possible angle of you having assisted the other person in the past.
If you are clean in this issue, write a letter to the HR and to the Recruitment Head as well. No need to keep in Anonymous. Anonymity works only when you are not the aggrieved party. In this case, if you maintain Anonymity it will work against you.