You should have mentioned your deadline before! Here, if not too late, is the multi-sheet solution in, as near as I can make it, your style. The error handling needs more work. Change the assignation of filePath to what you need.
Code:
Private Sub cmdFormatSheet_Click()
Dim xlApp As Excel.Application
Dim xlBook As Excel.Workbook
Dim xlSheet As Excel.Worksheet
Dim filePath As String
Dim arySheets() As String
Dim lngErrNumber As Long
Dim i As Integer
On Error GoTo cmdFormatSheet_Click_Error
'Set a reference to an Excel application.
On Error Resume Next
Set xlApp = GetObject(, "Excel.Application")
Select Case Err.Number
Case 0 'Excel application already running.
On Error GoTo cmdFormatSheet_Click_Error
Case 429 'Excel application not running so create it.
On Error GoTo cmdFormatSheet_Click_Error
Set xlApp = CreateObject("Excel.Application")
Case Else 'Some other run time error, so report it.
GoTo cmdFormatSheet_Click_Error
End Select
'If Excel has no workbooks then make it minimized.
If xlApp.Workbooks.Count = 0 Then xlApp.WindowState = xlMinimized
xlApp.Visible = True
'In normal course of events open the workbook minimized.
filePath = "C:\Users\Rod\Documents\Test.xlsx"
'filePath = "U:\Enrollment\Public\NEWBORN\" & strFileName & " " & Format(Now, "YYYY-MM-DD") & ".xls"
Set xlBook = GetObject(filePath)
xlBook.Windows(1).Visible = True
xlBook.Windows(1).WindowState = xlMinimized
'Redimension array with number of worksheets (base 0)
'Load worksheet names into array.
ReDim arySheets(xlBook.Worksheets.Count - 1)
i = 0
For Each xlSheet In xlBook.Worksheets
arySheets(i) = xlSheet.Name
i = i + 1
Next
'Select multiple worksheets and the cell range.
xlBook.Activate
xlBook.Sheets(arySheets).Select
xlBook.Sheets(1).Activate
Range("A1:M50").Select
'Format
With Selection.Font
.Name = "Arial"
.Size = 10
.Bold = True
End With
'Save and clean up.
xlBook.Close SaveChanges:=True
Set xlBook = Nothing
If xlApp.Workbooks.Count = 0 Then xlApp.Quit
Set xlApp = Nothing
MsgBox "Formatting successfully completed.", vbInformation
Exit_Procedure:
On Error GoTo 0
Exit Sub
cmdFormatSheet_Click_Error:
lngErrNumber = Err.Number
On Error GoTo 0
If Not xlApp Is Nothing Then
xlApp.Visible = True
xlApp.WindowState = xlNormal
End If
If Not xlBook Is Nothing Then
xlBook.Windows(1).Visible = True
xlBook.Windows(1).WindowState = xlMaximized
End If
MsgBox "Formatting failed with run time error " & lngErrNumber, vbCritical
Resume Exit_Procedure
Resume
End Sub