If you're unable to find a free PDF version of Santillana Ciencias Naturales 1, there are alternative options:
The Santillana series for 1st year (Primary or Secondary depending on the country) typically includes:
The most secure way to view these books is through Santillana's official portals, which often provide "Edupack" previews or digital licenses for students.
For students and teachers seeking Ciencias Naturales 1 Santillana