# How to get the coefficient list

polynomial=-x^4+2 b x^3+(b^2-c^2+2 c) x^2+(2 b c-2 c d) x+c^2-d^2


This is good

CoefficientList[polynomial, x]


But how to get coefficient list from the PolynomialForm?

I've tried this, but it does not give the coefficient list.

CoefficientList[PolynomialForm@polynomial,x]

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Closely related in the canonical Q&A is the last part of this answer by Verbeia. Perhaps that could be expanded to for example contain a "if you really have to" approach like the one by Anon below. –  Jacob Akkerboom Aug 17 '13 at 9:09
Do you require something like CoefficientList[#[[1]], x] &@PolynomialForm@polynomial? –  TomD Aug 17 '13 at 11:41

You cannot perform operations on a display type. Trying to operate on PolynomialForm is like trying to operate on TableForm. You're supposed to first do all the processing on your expression and then choose how you want to display it. If you absolutely have to do this, you have to first get the data inside PolynomialForm again and work on that, which can be done like this:
CoefficientList[PolynomialForm[polynomial] /. PolynomialForm[x_] :> x,x]