Form 8594 must also be filed if the purchaser or seller is amending an original or a previously filed supplemental Form. 8594 because of an increase or decrease.Enter your name and taxpayer identification number (TIN) at the top of the form. Then check the box for Purchaser or Seller. Form 8594 is a tax document required in certain business sales where the buyer acquires assets rather than stock or equity. Learn how to file form 8594 and when to file. The purpose of Form 8594 is to determine the treatment of the assets for tax purposes, establish the basis of the acquired assets for the purchaser. 1. Gather necessary documentation for the asset sale.