A file with .igs (Initial Graphics Exchange) extension is a 2D-3D design exchange file format that is independent of source or destination file format specifications used by CAD applications. It is used to exchange design information about circuit diagrams, wireframes, the freeform surfaces between two independent systems. IGS files can be opened by applications such as Autodesk, FreeCAD, CADEX CAD Exchanger, and other similar applications.
Docx is well-known format for Microsoft Word documents. Introduced from 2007 with the release of Microsoft Office 2007, the structure of this new Document format was changed from plain binary to a combination of XML and binary files. Docx files can be opened with Word 2007 and lateral versions but not with the earlier versions of MS Word which support DOC file extensions.
You can also convert IGS into many other file formats. Please see the complete list below.