Método 1:
$FileName = "Test.xlsx"
$startoffile = "C:\Tremble\"
Write-Host ($startoffile + $Filename)
Saída:
C:\Tremble\Test.xlsx
Método 2
$FileName = "Test.xlsx"
$startoffile = "C:\Tremble\"
#Write-Host ($startoffile + $Filename)
-join ($startoffile, $FileName), " "
Saída:
C:\Tremble\Test.xlsx