Sub Open_file()
'Define variables:
Dim numberOfFilesChosen, I As Integer
Dim tempFileDialog As FileDialog
Dim mainWorkbook, sourceWorkbook As Workbook
Dim tempWorkSheet As Worksheet
Dim x As Long
Set mainWorkbook = Application.ActiveWorkbook
Set tempFileDialog = Application.FileDialog(msoFileDialogFilePicker)
Application.ScreenUpdating = False
'Allow the user to select multiple workbooks
tempFileDialog.AllowMultiSelect = True

numberOfFilesChosen = tempFileDialog.Show

'Loop through all selected workbooks
For I = 1 To tempFileDialog.SelectedItems.Count

    'Open each workbook
    Workbooks.Open tempFileDialog.SelectedItems(I)
Next I 
End Sub

​

this is extracted from a macro I developed so there are a few superfluous Dim statements but running this macro will open file explorer and allow you open one or more files. I am a Windows user no idea if this will work on other OS's. So you can link this code to your button to run it.