I am looking for the way to implement MS Word plug-in for Mac and Windows. The plug-in should work with all versions of Microsoft Office (Microsoft Office 2003, Microsoft Office 2007, Microsoft Office 2010, Microsoft Office 2013, Microsoft Office 2016) and should work on Windows XP - Windows 10. It should work on MS Word on Mac also (at least on the latest versions).
It seems to be impossible to create one app for all of this OS and versions.
Description of the plug-in: The plug-in should help user to find the definition of any word (the definition will be in the beginning of this file or in the other file on the user's local disk). For example, user place mouse over word "math", a plug-in shows pop-up with definition "Mathematics (from Greek μάθημα máthēma, “knowledge, study, learning”) is the study of topics such as quantity (numbers), structure, space and change".
I am thinking about some variants of implementation.
First variant. I can make plug-in with help of WinForms and Microsoft.Office.Interopt for all Windows OS and versions of MS Office. I can create add-ins for Word on Mac with help of JavaScript. (Add-ins on JavaScript don't work on Microsoft Office versions < 2013).
Second variant. I can create plug-in with help of VBA for both platform and for all versions.
Are these variants possible? What the best way to create plug-in for Windows and Mac?
First variant. I can make plug-in with help of WinForms and Microsoft.Office ...
This, sound to me, way you should go if you would like to support older Office products (2010 and older). You would create VBA or COM/VSTO version for older versions on Windows. For older versions of Mac (ex:Entourage) you should consider AppleScript scripting extendability. Office Add-in (JS API) for newer versions on Windows and Mac together.
Second variant. I can create plug-in with help of VBA for both platform and for all versions.
No such thing as VBA add-on for Mac. You may efficiently use AppleScript for scripting certain actions in older Office for Mac.
This is all about your requirements. At the end you will make your decision. I would go with Office JS API as the start and later on see if you have strong demand of your app for older versions of Office.