Greetings Anonymous Monk,

You should start by having a look at Using Mathcad's OLE Automation Interface on the Mathcad website.
Having done a quick search of the site there seems to be quite a few results for OLE automation, which are perhaps worth a look. The references are for VB and VBA so you may find the ActiveState article How to convert a VBA macro to Perl helpful.

Failing that, you may find the module Win32::GuiTest useful, you could use it to drive the Mathcad application via SendKeys etc.

Hope this helps.

Martin