老师好！

打开Word文档时提示文档被锁定，有时提示被占用，这种情况怎样解决？

此主题相关图片如下：截屏图片.jpg


此主题相关图片如下：截屏图片 (1).jpg

主要代码如下：
\'\'\'
Dim st As String = ""      \'上传文件名
Dim dlg As New OpenFileDialog
dlg.Filter= "Word文件|*.doc;*.docx" \'设置筛选器
dlg.MultiSelect = True   \'多文件
If dlg.ShowDialog = DialogResult.OK Then
    For Each fl As String In dlg.FileNames       
        Dim str As String = ""
        Dim app As New MSWord.Application
        try
            Dim doc = app.Documents.Open(fl)
            For Each k As object In doc.Paragraphs
                If k.Range.text.trim().Contains("鲁") AndAlso k.Range.text.Contains("号") AndAlso k.Range.text.trim().Length < 20 Then   

                    str = k.Range.text.trim()
                    Exit For
                End If
            Next
            app.quit
        catch ex As exception
            msgbox(ex.message)
            app.quit
        End try
    Next
End If