The middle initial is A instead of C, but it's not unusual to be incorrect. In terms of enlistment dates and companies, this record is an exact match with Robberson File, who lived one house away from William C. File in 1850. William died June 15th and Robberson died August 2nd, near Richmond. That family lived in the vicinity of each other over the years, and as farmers, it's not likely they roamed as far as Mississippi.
This William File, of Concord NC never fought at Manassas.
Name: William A File
Residence: Cabarrus County, North Carolina
Occupation: Farmer
Age at Enlistment: 20
Enlistment Date: 31 Aug 1861
Rank at enlistment: Private
Enlistment Place: Cabarrus County, NC
State Served: North Carolina
Survived the War?: No
Service Record: Enlisted in Company C, North Carolina 33rd Infantry Regiment on 31 Oct 1861.
Mustered out on 15 Jun 1862 at Richmond, VA.
Birth Date: abt 1841
Sources: North Carolina Troops 1861-65, A Roster