DICOM Viewer is necessary to browse DICOM file generated by modality such as CR, CT, MRI, etc.
Normally DICOM Viewer connects to DICOM Server, that is software of managing DICOM file, and then it searches and gets image data and information of patient and examination.
Also, there are DICOM Viewer that can browse only local file without connecting feature to DICOM Server, as well.
SonicDICOM Media Viewer, available for free, is exactly this type of DICOM Viewer.
DICOM Viewer can simply browse these and it also can provide various features of adjusting brightness and contrast, pan/zoom, measurement, and others.