Form 8594 is a tax document required in certain business sales where the buyer acquires assets rather than stock or equity. 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. Buyer's accepted accounting practices. You must submit a paper filing and a supplemental form to the Assessor's Office. Both forms are on our e-filing site. Santa Clara County Retail Transactions and Use Tax.