Using PowerShell to insert BLOB into Oracle

I am trying to insert a PDF into a database as BLOB using the code below

  > [System.Reflection.Assembly]::LoadWithPartialName("System.Data.OracleClient")
    
    >
     $constr = "User Id=USER;Password=$password;Data Source=DB" 

Try { 
    >
     $filePath = 'C:\TEST PDF.pdf'  $Stream = Format-Hex -LiteralPath
    >
     $filePath   $queryString = "INSERT INTO TEST_TABLE (first_name, blob_data) VALUES (:one, :two)"  
   
    $connection = New-Object System.Data.OracleClient.OracleConnection($constr)  $connection.Open()
    
    $command = New-Object System.Data.OracleClient.OracleCommand($queryString, $connection)  
    
    $command.Parameters.Add("one", "SP_ERROR_ALERT") 
    $command.Parameters.Add("two", $Stream)  $command.ExecuteNonQuery() 
    $connection.Close() 
    }    Finally    {
    
            if ($connection -ne $null) 
            {
               $connection.Close()
               $connection.Dispose()
           }
     
            if ($command -ne $null) 
            {
               $command.Dispose()
            }   
    
    }

I have tried as many different ways I can think of but keep hitting an error complaining about the size of the BLOB. To test if would work I did an insert from another table containing Blobs and that worked fine - I therefore suspect my encoding.....

The error message I get is:

Exception calling "ExecuteNonQuery" with "0" argument(s): "Unknown datatype System.Object[] 
for parameter value of type Object."