Before we discuss the PDF, we must understand the man. Lipman Bers (1914–1993) was not just a calculus teacher; he was a titan of 20th-century mathematics. Born in Riga, Latvia, Bers survived the Soviet gulags and Nazi occupation before fleeing to the United States. He became a leading figure in complex analysis and a human rights activist.
The Internet Archive (archive.org) is a digital library. They often have scanned copies of out-of-print textbooks available for (usually 1 hour or 14 days at a time). Search for "Calculus Lipman Bers" on Archive.org. You will need a free account to "borrow" the scanned PDF. This is the most legal and ethical way to read a digital copy.