How to get filebytes from dt.row["FileName"].ToString()

Question

File.WriteAllBytes(Path.Combine(

ConfigurationManager.AppSettings.Get("DocumentPath").ToString(), randString + FileExtension), array[]);

 

 

 

i have a datatable which consist file name, from file name i want to know file bytes ,so that i pass a parameter into 

below function.

File.WriteAllBytes(Path.Combine(

ConfigurationManager.AppSettings.Get("DocumentPath").ToString(), randString + FileExtension), ?);