if all db's .mdf files are stored in this drive, you need to do DB Maintenance for all databases except that DB

DB Maintenance

----------------

shrink database

Delete backup history

and job history

Rebuild index

then you will get some free space in Drive. so you can do Shrink database and Rebuild index for database, which you are getting space issue in .mdf file.

or finally if you have another drive in the same server, you better to add .ndf files.