I have a medicine book in pdf format so its encrypted in that
format.The find program under that program is very scarn insufficient
for me.
Is there a way where can i use the find option program by terminal
where can i interact on it?

try pdftotext:

pdftotext myfile.pdf

creates a plain textfile named myfile.txt which you can view and
serach subsequently.

Or directly

pdftotext myfile.pdf - | grep <pattern>

This may or may not work for you. Reading "encrypted" I hear "password-
protected PDF file". In this case, you are out of luck.