Remove information permanently in PDF

Hi ,

I have many PDF files which i would like to send across to my collaborator.

Before that, i would like to remove "header and footer" in the document as  they contain identifiers.

I used "Set Page Boxes" to remove the hearder and footer of the PDF document (by setting the Top and Bottom margin value). 

However, during testing, my collaborator told me that he is still able to extract the information in the header and footer out as text.

May i know what is the correct way to remove "header and footer" of the document such that the info is also removed from the PDF itself. 

Thank you

Best Regards

BY