Round A4 up to a multiple of 4 total pages. I can't easily get the number of actual pages processed, so rely on telling the (rather hacky, and surprising - I have to divide to a separate counter to force an integer result) macro the number of pages used before the current numbering started.

--- a/docend.A4.tex	Tue Aug 06 22:24:02 2019 +0100
+++ b/docend.A4.tex	Tue Aug 06 23:29:51 2019 +0100
@@ -1,3 +1,4 @@
+\padpages{4}{8}
 \pagecolor{havocpurple}
 \thispagestyle{empty}
 \mbox{}