I know that Microsoft's OpenXML SDK is for .NET 3.5. I am looking for a .NET 2.0 library that could manage xlsx, docx formats. And can change the office format properties.
There is no library for 2.0. What you'll need to do is manually work with Open XML. First you'll need an unpacking/repacking function (not sure if WindowsBase which hosts System.IO.Packaging is available for 2.0, but you can use other zip utilities).