77 Pa. Stat. § 821
Within twenty days after a copy of any claim petition or other petition has been served upon an adverse party, he may file with the department or its workers' compensation judge an answer in the form prescribed by the department.
Every fact alleged in a claim petition not specifically denied by an answer so filed by an adverse party shall be deemed to be admitted by him. But the failure of any party or of all of them to deny a fact alleged in any other petition shall not preclude the workers' compensation judge before whom the petition is heard from requiring, of his own motion, proof of such fact. If a party fails to file an answer and/or fails to appear in person or by counsel at the hearing without adequate excuse, the workers' compensation judge hearing the petition shall decide the matter on the basis of the petition and evidence presented.
77 P.S. § 821