How to Install Package As Root User?

I’m trying to install: libpng12-0_1.2.50
I get the error: dpkg: error: requested operation requires superuser privilege

I try: su
Enter password:
I get an authentication error. (It is entered correctly for Admin user.)

Is the root password different than an Administrator password? If so, where/how do I get the root password?

sudo apt install libpng12

is there a usable version of libpng12-0 for pureos?

I have been trying to install this succesfully since i first got this laptop, constantly running into apps i cant run

libpng16-16 seems to exist.