How to fill the prompt in powershell script

There's no Password parameter, you can try with a .NET class:

$cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2
$cert.Import('C:\test.pfx','123456','DefaultKeySet')

Another option is to extend the abilities of Get-PfxCertificate, essentially enabling the password to be passed in.

# create a backup of the original cmdlet
if(Test-Path Function:\Get-PfxCertificate){
    Copy Function:\Get-PfxCertificate Function:\Get-PfxCertificateOriginal
}

# create a new cmdlet with the same name (overwrites the original)
function Get-PfxCertificate {
    [CmdletBinding(DefaultParameterSetName='ByPath')]
    param(
        [Parameter(Position=0, Mandatory=$true, ParameterSetName='ByPath')] [string[]] $filePath,
        [Parameter(Mandatory=$true, ParameterSetName='ByLiteralPath')] [string[]] $literalPath,

        [Parameter(Position=1, ParameterSetName='ByPath')] 
        [Parameter(Position=1, ParameterSetName='ByLiteralPath')] [string] $password,

        [Parameter(Position=2, ParameterSetName='ByPath')]
        [Parameter(Position=2, ParameterSetName='ByLiteralPath')] [string] 
        [ValidateSet('DefaultKeySet','Exportable','MachineKeySet','PersistKeySet','UserKeySet','UserProtected')] $x509KeyStorageFlag = 'DefaultKeySet'
    )

    if($PsCmdlet.ParameterSetName -eq 'ByPath'){
        $literalPath = Resolve-Path $filePath 
    }

    if(!$password){
        # if the password parameter isn't present, just use the original cmdlet
        $cert = Get-PfxCertificateOriginal -literalPath $literalPath
    } else {
        # otherwise use the .NET implementation
        $cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2
        $cert.Import($literalPath, $password, $X509KeyStorageFlag)
    }

    return $cert
}

And now you can call it

# tada: extended cmdlet with `password` parameter
Get-PfxCertificate 'C:\path\to\cert.pfx' 'password'

Also, if you still need the prompt, you can do something like this.

$pwd = Read-Host 'Please enter your SSL Certificate password.'
Get-PfxCertificate 'C:\path\to\cert.pfx' $pwd

There is now a Get-PfxData command in PowerShell that gets the certificate and chain. The command includes a -Password parameter that takes a SecureString object so you can avoid being prompted.

The EndEntityCertificates property contains an array of certificates at the end of the certificate chain and will contain the same certificate object created by the Get-PfxCertificate command.

The following example converts a normal string to a SecureString object, loads the certificates from a file, then assigns the first/only end certificate to the $SigningCert variable:

$SecurePassword=ConvertTo-SecureString -String "MyPassword" -AsPlainText -Force
$PfxData=Get-PfxData -FilePath ".\cert_filename.pfx" -Password $SecurePassword
$SigningCert=$PfxData.EndEntityCertificates[0]

You can now apply $SigningCert without being prompted for the password.