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.Form 8594 is a tax document required in certain business sales where the buyer acquires assets rather than stock or equity. Find the forms you need Choose Current year forms or Past year forms, and select By form number or By tax type. When and Where to File. The seller and purchaser must file Form 8594 as an attachment to their respective income tax return for the year in. A taxable asset purchase allows the buyer to "step up," or increase, the tax basis of the acquired assets to reflect the purchase price.