Harris County Tax Office Forms ; Vehicle Registration Forms. MV-506. Pdf, Emissions - testing regulations ; Property Tax Forms. TaxCertRequest.Which forms will I need to file? For Harris County Appraisal District, most businesses will need to file the general rendition form, 22.15. Affidavit of Motor Vehicle Gift Transfer. How to fill out the Harris County Tax Office Authorization Form? 1. Enter business or individual's name. 2. Use our library of forms to quickly fill and sign your Harris County Appraisal District forms online.