PowerShell - Invoke-WebRequest - How to use -Form option

Question

I get an error message when I use the 'FORM option with Invoke-WebRequest powershell utility. When I use help on the Invoke-WebRequest, I don't see the -FORM option listed. There is a Microsoft help document that shows an Example 6 with the -FORM option.

QUESTION - Is there something additional I need that supports the -FORM option for the PowerShell
Invoke-WebRequest utility? COMMENT - The PowerShell Invoke-WebRequest utility works fine for downloading a file.

Using PS version 5.1 on Windows 10.

Here's the script and error message.

$Uri = 'http://xxxxx.xxx.xxxx.xxx:8080/upload/upload.php'
$Form = @{
    file = Get-Item -Path 'C:\temp\xxxxxxx.pdf'
    nmbr = 'xxxxxxx'
}

Invoke-WebRequest -Uri $Uri -Method Post -Form $Form

------------------ ERROR MESSAGE -----------------------

Invoke-WebRequest : A parameter cannot be found that matches parameter name 'Form'.
At line:6 char:42
+ Invoke-WebRequest -Uri $Uri -Method Post -Form $Form
+                                                    ~~~~~
+ CategoryInfo          : InvalidArgument: (:) [Invoke-WebRequest], ParameterBindingException
+ FullyQualifiedErrorId :         
      NamedParameterNotFound,Microsoft.PowerShell.Commands.InvokeWebRequestCommand