We have tested these software vendors and approved them for use submitting S Corporation Informational and Composite Tax Returns. We only test software to ensure we can accept forms filed by the software. We are not associated with vendors and cannot guarantee any aspect of the software. Learn more about software approval from the IRS. Approved Software Vendors Blockworks Drake Software Lacerte My Tax Prep Office OLTPRO Desktop OLTPRO Web ONESOURCE ProSeries ProSystem FX TaxAct TaxSlayer Pro UltraTax CS If you need assistance with one of our online services, please email us at DORCustomerAssistance@mt.gov.