Finding a legitimate, free PDF of a specific academic textbook (especially a recent edition like 2021) is generally not possible through legal channels due to copyright restrictions. Publishers like PHI Learning typically restrict distribution to paid platforms.

Let’s address the elephant in the room. The search term strongly implies looking for a free downloadable PDF. While numerous websites (like Library Genesis, PDF Drive, or academia.edu) may host such files, you should consider the following:

The book "Pulse and Digital Circuits" is written by T. Yoganarasimhan and is a popular textbook for electrical engineering students. The book covers topics such as pulse circuits, digital circuits, and switching theory.

If you cannot find the Yoganarasimha PDF, these highly authoritative textbooks cover the same 2021 syllabus requirements: Pulse and Digital Circuits Overview | PDF - Scribd

Remember: A PDF is just a tool. Your understanding of pulse waveforms, time constants, and switching speeds is what will ultimately pass your exam or help you build a better circuit. Yoganarasimha’s book, especially the refined 2021 version, is your most reliable companion for that journey.