The old documents are still retrievable because they were properly archived.

retrievable 是由动词 retrieve（取回、检索）加上形容词后缀 -able 构成的形容词。retrieve 来自拉丁语，意思是"重新获得"或"找回"。加上 -able 表示"能够...的"，所以 retrievable 意思是"能够被找回/检索的"。