Send pdf as BASE64 encoded by Soap action

Hello.

I'm lost.

I have to encode a pdf document with BASE64.
And then send it to a webservice with soap action.

It is Navison runtime 5.01 - database vers. 3.7

I use the soap sdk and then somethink like this:

Print Report to pdf -->
SoapStart - with all parameters -->
SoapSerializer.WriteXml(STRSUBSTNO('<orderId>%1</orderId>',PostedInvoice."Your Reference"));
SoapSerializer.WriteXml(STRSUBSTNO('<status>%1</status>',4));
SoapSerializer.WriteXml(STRSUBSTNO('<pdf>%1</pdf>',pdffile));

And this is where I get lost - how do I both encode the pdffile to BASE64 and then include it?

Hope You can help me.

I have been searching this forum and I'm aware of the 99008516 codeunit, but I can't find out.
And I have installed the 'Commerce Gateway BTS Access Client'.Base64 component to try to encode the pdf.

Best regards.