Need to make the "NT Service\SQLAgent$SQL2012" a read permission on the needed file

Problem: 

Try to automate an SSIS job in SQL Server agent. The SSIS Service account is used, which is NT Service\SQLAgent$SQL2012 (for a named instance SQL2012 in my case). Got an error on open a local flat file.

Solution: 

Sharing the folder containing the file with the 'Everyone' group with a read permission as the virtual account 'NT Service\SQLAgent$SQL2012' is not possible to be explicitly selected.

Please note that, unlike the virtual account for SSAS, the virtual account for SQL Server Agent (i.e., SQLServerSQLAgentUser$MachineName$InstanceName) is not visible in the local user and group list (see this for details). So we cannot give the virtual account a read permission as we do for the virtual account for SSAS service account.