Just realized that GroupDocs.Viewer is unable to detect password protected 7z archive as well.
Test code - password protected 7z archive shows Encrypted = False, but password protected zip archive shows Encrypted = True:
Using FileDialog As New OpenFileDialog
If FileDialog.ShowDialog() = DialogResult.OK Then
Using Viewer As GroupDocs.Viewer.Viewer = New GroupDocs.Viewer.Viewer(FileDialog.FileName)
Dim FileInfo As GroupDocs.Viewer.Results.FileInfo = Viewer.GetFileInfo()
MsgBox($"Encrypted = {FileInfo.Encrypted}")
End Using
End If
End Using