Thaddeus and Kelly are both employees at S&S$,$ a retail store. One$-$night Thaddeus steals $$10,000$ from the store safe. S&S knows nothing of the theft. But, unbeknownst to Thaddeus, Kelly secretly witnessed the theft. Thereafter, Kelly creates, dates, and signs a document called $$Agreement$.$ It states: I, Kelly, hereby agree not to report to S&S management or any law enforcement agency, the activities and conduct on the part of Thaddeus on the evening of March $11,2023$ between the hours of $6$ and $7$ p$.$m$.$ In exchange for which Thaddeus promises to pay to me$,$ Kelly, $$5,000$ within $24$ hours.

Kelly presents the document to Thaddeus and says $$Sign or I will report you to the police. You know very well what I$$m talking about.$$ Thaddeus reads the document and signs it$.$

Do the parties have a contract? May Thaddeus void the contract?