by Matthias Beck et al. is an open textbook available for download on GitHub.

A companion to the eTextbook, the Wolfram U Introduction to Complex Analysis provides free video lessons, interactive notebooks, and quizzes. Open-Source Textbooks:

There is no single " Complex Analysis with Mathematica " ebook that is officially free for permanent download as a full textbook from its primary publisher. However, several legitimate alternatives and official free resources provide similar content or interactive experiences. Legitimate Free eBooks and Resources