HI,
try this:
Dim directory As [String] = "C:\Whatever\"
Dim linesA As [String]() = File.ReadAllLines(Path.Combine(directory, "FileA-Database.txt"))
Dim linesB As [String]() = File.ReadAllLines(Path.Combine(directory, "FileB-Database.txt"))
Dim onlyB As IEnumerable(Of [String]) = linesB.Except(linesA)
File.WriteAllLines(Path.Combine(directory, "Result.txt"), onlyB)