Hi Neha,
An MRC file is a density map format.  You cannot save it as an atomic model, because it does not contain atomic coordinates. 

There is no tool in Chimera to create atomic structure instantly from a map.   Researchers use various programs to build atomic structures into a map or to build an atomic model separately and then fit it into a map, but it is generally an interactive process that takes many steps.  I am not an expert on this process, but you could read hundreds of research papers "Methods" sections to see descriptions of the ways in which it is done.

Regards,
Elaine
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Elaine C. Meng, Ph.D.                       
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On May 10, 2021, at 10:24 AM, Neha Goel <nehagoel24march@gmail.com> wrote:
>
> Dear Chimera,
> I have a .mrc file. I reopened the file in chimera and would like to save it in pdb. I am unable to save it. It needed the molecular model pdb. Kindly guide me the way to save it.
> Regards
> Neha Goel