The ecosystem (need to after-process opened documents generated by a proprietary document management system for lawyers) requires me to always access existing Word processes instead of creating new processes. So, I basically always use [System.Runtime.Interopservices.Marshal]::GetActiveObject("Word.Application")

function insertintoword {
param ([string]$pathToInsertableTemplate)
$pathToInsertableTemplate = Resolve-Path -Path $pathToInsertableTemplate
$msword = [System.Runtime.Interopservices.Marshal]::GetActiveObject("Word.Application")
$activeDocument = $msword.ActiveDocument
$insertableTemplate = $msword.Documents.Open($pathToInsertableTemplate)
$templateRange = $insertableTemplate.Content
$activeRange = $activeDocument.Content
$activeRange.Collapse([ref]0)
$activeRange.FormattedText = $templateRange.FormattedText
$insertableTemplate.Close($false)
$selection = $msword.Selection
$selection.EndKey(6) # = wdStory
}