Stamp Tax Act Article 4

Documents subject to the levy of stamp tax shall be retained for at least two years after the rights and obligations provided in said document cease to exist. But for publicly owned enterprises or joint ventures of public and private enterprises, the duration of retention shall accord to the provisions of the Accounting and other relevant regulations.
中文原文 印花稅法第4條
應納印花稅之憑證,於權利義務消滅後應保存二年。
但公營或公私合營之事業,應依照會計法及其他有關法令之規定辦理。

English translation for reference only; the Chinese text prevails. Not legal advice.