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. Allegheny County Central TCD Version If you lived in any of these PSD Codes at any point in the year, you must file this form (Replaces PGH-40). Learn how to file form 8594 and when to file.