VBA跨模块调用已打开Word文档报错，求最优解决方案

我需要在Word文档中编写内容，必要时在另一个文档撰写段落，关闭该文档后，将段落复制到始终处于打开状态的第一个文档中，但尝试多种方法均失败：

尝试的方法及报错 #

方法1 #

执行以下代码：

Dim wdDocMain As Word.Document
Set wdDocMain = ActiveDocument

收到运行时错误4248：该命令不可用，因为没有打开的文档。

方法2 #

执行以下代码：

Dim wdDocMain As Word.Document
Set wdDocMain = wdApp.Documents.Open(FileName:=pathmaindoc, ReadOnly:=False, Visible:=True)
wdDocMain.Activate

收到运行时错误91：对象变量或With块变量未设置。

临时非最优解决方案 #

关闭已打开的文档后重新打开，代码如下：

Set wdDocMain = wdApp.Documents.Open(FileName:=pathmaindoc, ReadOnly:=False, Visible:=True)

补充代码片段 #

主过程代码 #

Dim wdapp As Word.Application
Dim wdDoc As Word.Document

Set wdapp = New Word.Application
Set wdDoc = wdapp.Documents.Open(FileName:=PathName_HiveDown_Creation, ReadOnly:=False, Visible:=True)
wdapp.Visible = True

调用模块的代码 #

当满足特定条件时，调用模块copyparafromtemplatetomain：

pathmaindoc = PathName_HiveDown_Creation
pathtemplatedoc = PathName_Template
'wdDoc.Close savechanges:=True
copyparafromtemplatetomain 

模块代码 #

Public wdapp As Word.Application
Public wdDocMain As Word.Document

Sub copyparafromtemplatetomain(pathmaindoc As Variant, pathtemplatedoc As Variant, paramain As Variant, paratemplate As Variant, index As Integer)
        
    Dim wdDocTemplate As Word.Document
    
    Dim PathName_MainDoc As Variant
    PathName_MainDoc = pathmaindoc

    Set wdDocMain = wdapp.ActiveDocument

此处收到运行时错误91，仅关闭主过程中的文档后代码才能运行。

内容的提问来源于stack exchange，提问作者Yannis