We present an external portable module for transforming bright-field microscopy to differential interference contrast (DIC) microscopy and digital holographic microscopy together. The module is composed of simple optical elements, positioned between the microscope output plane and the digital camera plane; thus, it can be integrated externally with existing microscopes. The proposed module enables polarization DIC imaging, without special polarization elements, under either white-light or coherent illumination, providing label-free imaging of biological samples, as recorded directly by the digital camera. In addition, by rotating one element inside the module, an off-axis hologram is created on the camera under coherent illumination, thus providing the possibility for reconstruction of the quantitative phase profile of the same sample. The method is demonstrated for imaging silica microspheres and biological cells.