This does not seem to work (it prints the table as a header):
<f:facet name="header">
<p:font size="8">
<p:footer borderWidthTop="1" borderColorTop="blue">
<p:table columns="3">
<p:cell>Why Seam?</p:cell>
<p:cell>Why Seam?</p:cell>
<p:cell>Version 1.0</p:cell>
</p:table>
</p:footer>
</p:font>
</f:facet>
Omitting the <p:table> like this does work (it prints it as a footer):
<f:facet name="header">
<p:font size="8">
<p:footer borderWidthTop="1" borderColorTop="blue">Why Seam?</p:footer>
</p:font>
</f:facet>
this is a restriction of the implementation. You could do something with facet="header", but at the moment imho pdf generation through tags is not very mature yet. Although iText is quite fast, its roots are ancient and it shows.