Update for version 16 :

You need to define your own paperformat, and call that paper to action.
Adjust the margin_top to eliminate the header and margin_bottom value for the footer

<record id="custom_paper" model="report.paperformat">
    <field name="name">custom paper formatfield>
    <field name="default" eval="True" />
    <field name="format">A4field>
    <field name="page_height">0field>
    <field name="page_width">0field>
    <field name="orientation">Portraitfield>
    <field name="margin_top">7field>
    <field name="margin_bottom">7field>
    <field name="margin_left">7field>
    <field name="margin_right">7field>
    <field name="header_line" eval="False" />
    <field name="dpi">90field>
record>

Note : please fix the code above, especially the closing field. Tried many times to fix this answer but not works. This forum is messed up it can't save code block above properly.

Best regards,

Altela (altelasoftware.com)