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. 1. Gather necessary documentation for the asset sale. 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.