Wisconsin law requires that the original will be filed within a short time after death; see Section 856.05 of the Wisconsin Statutes for requirements and penalty. Because a court procedure is required it is recommended that you consult with an attorney as soon as possible. Faiulure to act timely may result in some sort of equitable estoppel, laches, ec. so do not set on rights. .
Attorney Jinkins is correct. Please retain an attorney who can make sure that the will is properly filed with the probate court. Once it is there, it is a public record and can be reviewed by anyone.
As for whether it is "legal to change a will when a person is drugged," this depends on whether your father had testamentary capacity at the time of the signing of the document. The medical records would need to be reviewed, witnesses interviewed, etc. in order to determine whether the will could be challenged based upon a lack of testamentary capacity. Good luck to you.
This information is presented as a public service. It should not be construed to be formal legal advice nor considered to be the formation of a lawyer/client relationship. I am licensed in Connecticut and New York and my answers are based upon the law in those jurisdictions. My answer to any specific question would likely be different if I were to review a client's file and have the opportunity to interview the client. Accordingly, I strongly urge you to retain an attorney in your jurisdiction with respect to any legal matter.