Meshmixer is a free 3D sculpting-based CAD (Computer Assisted Design) program created by Autodesk as part of their “123D” software line
This software is often used for preparing mesh models for 3d printing and is useful for fixing non-manifold models, remeshing models, and most often to generate supports for printing.
If you want to export a model for use with mesh mixer you will need export as either an OBJ or PLY file format
An OBJ file is a standard 3D image format that can be exported and opened by various 3D image editing programs. It contains a three-dimensional object including 3D coordinates, texture maps, polygonal faces, and other object information.
PLY is a computer file format known as the Polygon File Format or the Stanford Triangle Format. It was principally designed to store three-dimensional data from 3D scanners.
3D Mesh- Maya
Autodesk Maya is an industry leading 3D animation software application developed by Autodesk that enables video professionals who work with animated film, television programs, visual effects, and video games to create highly professional three-dimensional (3D) cinematic animations.
If exporting 3d models from Pix4d into Maya it is recommended to use a flat light or the model may not look the same as in pix4d