Open PDF

$webApp = Get-SPWebApplication http://url
If ($webApp.AllowedInlineDownloadedMimeTypes -notcontains "application/pdf")
{
  Write-Host "Adding PDF MIME Type..."
  $webApp.AllowedInlineDownloadedMimeTypes.Add("application/pdf")
  $webApp.Update()
  Write-Host "MIME Type saved."
} Else {
  Write-Host -ForegroundColor red "PDF MIME type is already added."
}