You need the unarchive_cmd
option described in this blog post:
http://blogs.splunk.com/2011/07/19/the-naughty-bits-how-to-splunk-binary-logfiles/
Alternatively, you can do a scripted input
or a scripted lookup
where you call another utility to convert to a plain text format (like HTML):
http://docs.splunk.com/Documentation/Splunk/latest/AdvancedDev/ScriptedInputsIntro
http://docs.splunk.com/Documentation/Splunk/6.4.1/Knowledge/Configureexternallookups
Here are some that can help (I have NOT tried any of them):
http://dbf-file-viewer.soft112.com/
http://dbfviewer.com/