Conversation so far:
What is the background of Tosca?
In the early 1880s, the French playwright Victorien Sardou began a collaboration on Tosca with actress Sarah Bernhardt, whom he provided with a series of historical melodramas.
Did Sarah Bernhardt play a role in Tosca?
Sarah Bernhardt starred in La Tosca throughout Europe
Where did Sarah Bernhardt and Victorien Sardou take La Tosca in Europe?
Tosca premiered in Paris, with more than 3,000 performances in France alone. Tosca had played in both Milan and Turin, as well as across Europe.
How was the play Tosca received?
Tosca was an outstanding success, with more than 3,000 performances in France alone
What made the play Tosca so popular?
Is there anything else interesting about the background of the Tosca opera?
Giacomo Puccini wrote to his publisher, Giulio Ricordi, begging him to get Sardou's permission for the work La Tosca to be made into an opera

Question: Why did he need Sardou's permission?
Self-contained rewrite: Why did Giacomo Puccini need Sardou's permission to make La Tosca into an opera?