Encode PFX as Base64

base64pfx.ps1

# path to file
$fileName = "C:\tmp\mycert.pfx"

# get content of the file as Byte
$fileContentBytes = get-content $fileName -Encoding Byte

# convert to Base64
$fileContentEncoded = [System.Convert]::ToBase64String($fileContentBytes)

# convert to secure string
$secret = ConvertTo-SecureString -String $filecontentencoded -AsPlainText -Force

# store the secret in KeyVault
Set-AzureKeyVaultSecret -VaultName $vaultName -Name $certificateName -SecretValue $secret