Please recommend application to open, edit and 'Save As' JSON files as .JSON & .TXT files (Windows7)

I have to read .JSON files created by another application. Those .JSON files certainly worked, delivering data to web-based application.
Now I've lost the application on my PC that I used to READ those JSON files (Windows 7).  I used it 4 years ago - and I think it was 'Eclipse'.

My objectives are to:
- handle .JSON files of upto 500kb (usually <200)
- Test for well-formed .JSON files
- 'Save As' edited my.JSON file as myNew.JSON
- 'Save As' edited my.JSON file as text file
- Familiarise myself with detailed structure from JSON files I receive from another application, and experiment with effects of Adding/changing .JSON content.
- The ability to annotate edits in JSON and print out a record would be helpful, to have a record to changes which cant be lost or misunderstood.

* Interconversion between JSON and XML is NOT required.

Private work; freeware preferred, but rapid success very pressing.

I looked for 'JSON readers', as web extns on Google store etc.. and was discouraged by patchy recommendations, and difficulty in assessing if they would do what I want.

My background is limited: VBA customisation of Excel to drive automation of Visio drawing functions in much detail; but little other experience. So I need appl with reasonable documentation.

I'd be grateful for your guidance.

Thanks
Kelvin4