Mail merge into a Word document generates Error Code 4248 - excel

Question

My goal is to use two dropdown menus (DM) within a workbook to open a filled-out document.
The DM 1 is to select which row of data will be merged.
The DM 2 is to select which template is being used.
I have separate code that highlights the selected row and opens the document.
Set doc = appWD.ActiveDocument gives me
error 4248 This command is not available because no document is open.
The template is open when I receive this error.
For Context:
Open_LPA_Template, run by itself, does open the Word document selected from the DM 2.
Select_Parcel, run by itself, does highlight the row of data selected from the DM 1.
Sub Run_Mail_Merge_LPA()
Dim doc As Word.Document
Dim appWD As Object
Dim wb As Workbook
Dim ws As Worksheet
Dim ws2 As Worksheet
Dim tbl As ListObject
Dim row As ListRow
Dim searchValue As String
Dim searchRange As Range
Dim foundCell As Range
' Get references to the workbook and worksheets
Set wb = ThisWorkbook
Set ws = wb.Worksheets(1)
Set ws2 = wb.Worksheets(2)
' Create an instance of the Word application
Set appWD = CreateObject("Word.Application")
' Open the Word document that has been selected in DM 2
Open_LPA_Template
' Select_Parcel's CODE: Select the Row of Data from DM 1 for the Mail Merge
ws2.Select
' Select cell D3 in worksheet 2
ws2.Range("D3").Select
' Store the value in D3 of worksheet 2 in a variable
searchValue = ws2.Range("D3").Value
' Set the search range to the entire column A of worksheet 1
ws.Select
Set searchRange = ws.Range("A:A")
' Use the Find method to search for the search value in the search range
Set foundCell = searchRange.Find(searchValue)
If Not foundCell Is Nothing Then
' If a match is found, select the cell
foundCell.Select
ActiveCell.EntireRow.Select
Else
' If no match is found, print a message
Debug.Print "Value not found in column A"
End If
' MAIL MERGE CODE: Set the active document to the Word document that was opened
Set doc = appWD.ActiveDocument
' Perform the mail merge
doc.MailMerge.MainDocumentType = wdFormLetters
doc.MailMerge.OpenDataSource _
Name:=row.Range, _
ConfirmConversions:=False, ReadOnly:=False, LinkToSource:=True, _
AddToRecentFiles:=False, PasswordDocument:="", PasswordTemplate:="", _
WritePasswordDocument:="", WritePasswordTemplate:=""
doc.MailMerge.Execute
End Sub
Sub Open_LPA_Template()
Dim wb As Workbook
Dim ws As Worksheet
Dim ws2 As Worksheet
Dim MainPath As String
Dim MainPath2 As String
Dim MainPath3 As String
Dim MainPath4 As String
Dim MainPath5 As String
Dim MainPath6 As String
Dim Parcel As String
Dim fileName As String
Dim FullPath As String
Dim mWord As Object
Set wb = ThisWorkbook
Set ws = wb.Worksheets(1)
Set ws2 = wb.Worksheets(2)
Set appWD = CreateObject("Word.Application")
appWD.Visible = True
MainPath = "C:\Users\ME\Dropbox (ORC)\Desktop\Templates\LPA\"
MainPath2 = "C:\Users\USER1\Dropbox (ORC)\Desktop\Templates\LPA\"
MainPath3 = "C:\Users\USER2\Dropbox (ORC)\Desktop\Templates\LPA\"
MainPath4 = "C:\Users\USER3\Dropbox (ORC)\Desktop\Templates\LPA\"
MainPath5 = "C:\Users\USER4\Dropbox (ORC)\Desktop\Templates\LPA\"
MainPath6 = "C:\Users\USER5\Dropbox (ORC)\Desktop\Templates\LPA\"
fileName = ws2.Range("E3")
' Check if the file exists at the first path
If Dir(MainPath & fileName & ".docx") <> "" Then
FullPath = MainPath & fileName & ".docx"
ElseIf Dir(MainPath2 & fileName & ".docx") <> "" Then
' If the file does not exist at the first path, check the second path
FullPath = MainPath2 & fileName & ".docx"
ElseIf Dir(MainPath3 & fileName & ".docx") <> "" Then
' If the file does not exist at either of the first two paths, check the third path
FullPath = MainPath3 & fileName & ".docx"
ElseIf Dir(MainPath4 & fileName & ".docx") <> "" Then
' If the file does not exist at any of the first three paths, check the fourth path
FullPath = MainPath4 & fileName & ".docx"
ElseIf Dir(MainPath5 & fileName & ".docx") <> "" Then
' If the file does not exist at any of the first four paths, check the fifth path
FullPath = MainPath5 & fileName & ".docx"
Else
' If the file does not exist at any of the first five paths, use the sixth path
FullPath = MainPath6 & fileName & ".docx"
End If
appWD.Documents.Open (FullPath)
There are six paths because it could be accessed/used by six people who get to the shared Word documents through their own computers.

Answer 1

Since you are creating a new instance of Word via
Set appWD = CreateObject("Word.Application")
That Word instance has no open documents. You need to open the relevant document and address it via code like:
Set doc = appWD.Documents.Open(Filename:="C:\Users\Aaron Bradow\Documents\Mail Merge Document.docx", AddToRecentFiles:=False, ReadOnly:=True)

Answer 2

The problem is that you create two separate instances of Word Application in the code and try to access a Document instance opened in another Word Application instance/process. If you want to use the ActiveDocument property you need to deal with a single Word Application instance in the code. So, you may pass a created Word Application instance as a parameter to the method to open files.
Be aware, the Documents.Open function from the Word object model opens the specified document and adds it to the Documents collection. It also returns a Document object which can be used instead of the ActiveDocument property in the code.
Sub OpenDoc()
Dim doc As Word.Document
Set doc = Documents.Open FileName:="C:\MyFiles\MyDoc.doc"
End Sub