Is this considered immoral or stealing if I take another person's book and rewrite a christian version of it?

I was going to do this but I feel weird in my spirit, as if I'm trading my morals for money by profiting from somebody else's work. I have not even read the book I bought, I just took the outline, and improved on it and want to innovate totally new ideas in my version but the fact I almost stole somebody else's outline, makes me think it might be considered unethical, even if it's not stealing as a criminally punishable offence since it's so different from the original. It might be easy money and it might be attainable money, but it seems immoral.

Is this considered immoral or stealing if I take another person's book and rewrite a christian version of it?
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