Set and Reset Windows File Associations

Windows File Association also known As Default Programs allows you to tell Windows what program you would like to use to open a specific file type.
 

Setting File Associations to Open In AcroPlot Matrix

This is the easy part.  Just run AcroPlot Matrix then choose the Edit > Set File Associations.  The Default Programs dialog box should appear and you can pick which extensions you would like to associate with the program.
 
 
 

Resetting File Associations to open in a different program.

Unfortunately Windows does not make it easy to reset the File Associations.  We have never understood why except that Microsoft tends to do lots of stupid stuff to make it hard for the user.  It would be very simple for them to cache what the old value was and allow you to uncheck one or all of the values on the Default Programs Dialog but they actually gray out the ones which you have set to open with a program..
 
Instead you need to run the Control Panel > Programs > Default Programs > Set Associations dialog.  You can also in Windows 8 find it by searching for Default Programs and then selecting the "Associate a file type or protocol (such as .mp3 or http://) always open in a specific program" option.  Both of these will take you to the File Association Dialog which you will have to pick each extension you would like to change and then use the button in the upper right to "Change Program.." and select a program from the list.  If the program you want to use is not shown in the list you can always browse to it.