VBA Declaring arguments outside a function - excel

Question

I have vba code which opens a word document based on a template and when finished, runs the code below:
Public Sub Destroy(doc As Word.Document, app As Word.Application)
If Not (doc Is Nothing) Then doc.Close SaveChanges:=wdDoNotSaveChanges
If app.Documents.Count = 0 Then app.Quit wdDoNotSaveChanges
Set app = Nothing
End Sub
(this means that the app only closes if there are no other documents open and doesnt leave a blank application loaded when finished either)
I would like to extend this to excel and possibly other applications in the future; but rather than write a separate function for every different application, I wondered if I could have one function do-it-all.
The problem I'm finding is the declaration of arguments "doc As Word.Document" and "app As Word.Application".... is there a way of declaring what "doc" and "app" are in the calling program, and then getting the type definition of them inside my function to decide what to do depending on what type of application I choose to destroy()?
Edit:
I'm happy with the code, but on running a quick test in the code below, I founf that byref and byval both didnt effect the value of myval:
Private Sub Command12_Click()
Dim myval As Integer
myval = 1
MsgBox "the value of myval is " & myval
doByVal (myval)
MsgBox "the value of myval is " & myval
doByRef (myval)
MsgBox "the value of myval is " & myval
End Sub
Private Sub doByVal(ByVal a As Integer)
a = a + 1
MsgBox "byVal gives " & a
End Sub
Private Sub doByRef(ByRef a As Integer)
a = a + 1
MsgBox "byRef gives " & a
End Sub

Answer 1

Sure. You may declare generic Objects as args of the function, and verify their actual type in function. Basically, your code frame will look like:
Public Sub Destroy(ByVal doc As Object, ByVal app As Object)
If (TypeOf doc Is Word.Document) And (TypeOf app Is Word.Application) Then
' Word related stuff
ElseIf (TypeOf doc Is Excel.Workbook) And (TypeOf app Is Excel.Application) Then
' Excel related stuff
' ...
Else
' Do something about mixed cases, unhandled types etc.
End If
End Sub
And here's passing args to Destroy function, as (a bit exaggerated) example:
Dim my_doc As Excel.Workbooks
Dim my_app As Excel.Application
Set my_app = Excel.Application
Set my_doc = my_app.Workbooks("IWantYouClosed.xlsx")
Call Destroy(my_doc, my_app)

Answer 2

You are trying to use Early binding, and that requires creating a reference to the appropriate library (in Tools, References).
Alternatively, you can use Late binding, declaring doc As Object.
The web has lots of pages on "early binding vs late binding". One sample here.

Answer 3

Using the help given, this is the code I am now using, hope this helps someone.
Public Sub Document(ByVal doc As Object, ByVal app As Object)
Select Case True
Case (TypeOf doc Is Word.Document And TypeOf app Is Word.Application)
If Not (doc Is Nothing) Then doc.Close SaveChanges:=wdDoNotSaveChanges
If app.Documents.Count = 0 Then app.Quit wdDoNotSaveChanges
Set app = Nothing
Case (TypeOf doc Is Workbook And TypeOf app Is Excel.Application)
'code for excel workbook
Case Else
MsgBox "Cannot recognise the document/application, or there may be a mismatch"
End Select
End Sub