old style; old format; old-structure form
Refers to something that follows an older pattern, structure, or convention, often contrasted with a newer version.
This document is in the old format, so please rewrite it in the new style.
Old-style contracts may sometimes have legal issues.
旧式 also means 'old style' but often implies outdated or obsolete, whereas 旧形式 is more neutral and simply refers to an older form.
Compound of 旧 (old) and 形式 (form, format). The reading is the standard on'yomi combination.