If you cannot find a free PDF legally, buy the physical book from Karnatic Music Book Centre (Chennai) or Giri Trading . It is inexpensive and much easier on the eyes than a screen scan.
Sangeetha Bala Padam is a fundamental instructional book for Carnatic music, typically used by beginners to learn the basic exercises (Varisais), Geethams, and early-stage Varnams. Accessing the PDF Sangeetha Bala Padam Varnam Pdf