The invention discloses a method and a device for encrypting an official document and a method and a device for verifying the official document. The method for encrypting the official document comprises the following steps of: performing digest operation on a text of the official document to acquire digest information of the text; generating corresponding digital watermark information according to the digest information; and embedding the digital watermark information into the text and an official seal of the official document respectively. The method for verifying the official document comprises the following steps of: extracting first digital watermark information and second digital watermark information from the text and the official seal of the official document respectively; performing the digest operation on the text of the official document to acquire the digest information and generating third digital watermark information according to the digest information; and comparing the first digital watermark information, the second digital watermark information and the third digital watermark information, verifying the official document to be a legal official document if the three pieces of information are consistent, and verifying the official document to be an illegal official document if the three pieces of information are inconsistent. In the invention, the text and the official seal of the official document are associated with each other by embedding the same digital watermark information, so that the safety is improved; and the information is embedded by a digital watermark algorithm, so that a watermark is more easily and conveniently embedded and detected, and the requirements on hardware facilities are reduced.