Quick and Dirty:
from mpack tools:
munpack YOURMAILFILE
sigtool --md5 ../XFILES/DocumentXNoX1076196.xls >> MYSIG.hdb
Better:
https://objective-see.com/blog/blog_0x17.html
https://www.decalage.info/vba_tools
https://www.decalage.info/python/olevba
http://www.pwnage.io/2013/06/fun-with-clamav.html?m=1
http://blog.clamav.net/2011/02/how-to-create-custom-signatures-for.html?m=1
http://blog.adamsweet.org/?p=250
https://packages.gentoo.org/packages/net-mail/mpack
https://www.idrsolutions.com/online-pdf-to-html5-converter/
http://blog.talosintelligence.com/2008/09/logical-signatures-in-clamav-094.html
http://hexacorn.com/d/PESectionExtractor.pl
Click to access signatures.pdf
http://hiddenillusion.blogspot.de/2012/06/xdp-files-and-clamav.html