That’s an interesting question!

I found this:

The Song's imperial successors, and especially the Ming (A.D. 1368-1644), endeavored to strengthen state control of publication, although relatively few changes were made to the formal structure of regulation until the Qing. Each post-Song dynastic code specifically forbade the unauthorized republication of governmental works on astronomy, the civil service examinations, and other materials long considered sensitive. Additionally, each contained provisions banning "devilish books." These provisions were supplemented periodically by special decrees— as may be seen, for example, in the Hongwu Emperor's (1368-92) orders that all works disparaging the newly founded Ming dynasty even indirectly through the use of homophonic puns be eliminated," and in the Qianlong Emperor's (1736-96) famous decree of 1774 requiring that all literature be reviewed so that any books containing heterodox ideas could be destroyed.

Alford, William P.. To steal a book is an elegant offense: intellectual property law in Chinese civilization. 1995.