Obtain a blank Form 503, Assumed Name Certificate. The forms are available from the Texas Secretary of State, or by downloading and printing a copy directly from the Internet. You or a legal representative -- such as an attorney or registered agent -- may fill out the form.
Complete items one through four. You will need the proposed assumed name; the legal name of the entity or individual filing the certificate; your type of business organization -- that is, sole proprietorship, partnership, LLC, etc.; and any file number, if one exists, assigned to that business by the Texas Secretary of State.
Complete items five through seven with the following: the jurisdiction of your main office, whether it's in Texas or not; the office address of that location; the office address of your principal location in Texas, if your main office is not in Texas. Complete item eight with foreign address information, if necessary, according to the instructions that come with the form.
Complete item nine, the duration of use of the assumed name -- the maximum duration is 10 years. Complete item ten, naming the county or counties in which the assumed name will be used.
Sign and date the form. The signature may be that of the individual operating the business or a legal representative of the business. Return the form with the $25 filing fee to the Secretary of State, P.O. Box 13697, Austin, TX 78711-3697. Also file the certificate with the county clerk in the county where you have your principal place of business, or registered office in Texas if your principal place of business is outside the state. Clerk's fees for such filings vary by county.