Replace the font of a given pdf

I would like to replace the font of a pdf and I just have no clue to set forth on it

I see the font name, ie ''Courier-New'' then I change all of such instances throughout the pdf into i.e NewTimesRoman but my pdf, sure enough it just doesn't open with pdfreader all is just blank and blank

Could you help me?? Please

Thank you, sorry for bad english too as i am learning it not naturally abusing it

Replace the font of a given pdf

How are you changing the font? If you are using Acrobat, please post in the Acrobat forum.