.ISA File

The isa file extension is related to Adobe ImageReady bitmap graphic editor that was part of Adobe Photoshop up until version CS3.

The isa file contains ImageReady action. Actions are basically macros which are used to automate certain task with single click. 

How to open:

You can use ISA actions in ImageReady editor of some earlier versions of Adobe Photoshop.

How to convert:

It is unlikely that Photoshop action files (.isa) can be converted to anything else.