File API not working in IE11

I am working on a legacy maintenance project. The project that I am working on needs to be run on IE11. The project that I am working on has versions say, V1 and V2. Both are expected to run on IE11.

Somewhere in code of V1, I am checking for the file API properties like, window.File, window.FileReader. But, I am always getting value undefined for these properties.

But, for version V2, File API is working perfectly fine. I do not get undefined value for window.File in V2.
The problem is, I do not have access to the V2 project. And I am still not getting what is missing in V1 which failing window file APIs.

Do you have any idea? Or Did you ever face such problem earlier?
Thank you in advance.