If you are looking for Shankara’s actual writings ( Bhashyas or commentaries), these are the standard texts often sought for study:

A short, 68-verse treatise perfect for beginners. It uses simple metaphors to explain the nature of the soul. A Sanskrit-English version is hosted by Estudante da Vedanta .

The most acclaimed modern biography and philosophical review for download is by Pavan K. Varma. Review of " Adi Shankaracharya: Hinduism's Greatest Thinker "

Reviewers on VAK1969 note that Varma uses an accessible, sometimes anecdotal style that makes dense philosophical concepts like Maya (illusion) and Brahman (ultimate reality) easier to understand.

It includes a "Virtual Tour" of the four major Mathas and discusses how Shankara’s teachings align with modern scientific concepts.