SMB : TCP/445 impossible to sniff a document sent to be printed to a MS Spooler Server

Hi all, 

I'm focused on SMB sniffing: TCP/445 and I have basic architecture:
( PC --> Microsoft spooler server:TCP/445 --> Printer )

I would like to prove that it's possible to capture and decrypt all document sent by the PC to Microsoft Spooler server to be printed. 

With Ethereal/SMBspy or just tcpdump/tcpflow, it's possible to capture the data exchanged between the client and server ( PC --> spooler:TCP/445 ), but it’s a SMB file. In some case (with SMBspy, you can obtain a data file, which contain a PCL format file, but impossible to use it.

I tested SMBsniffer but it obtained just a result for file exchange between PC / Windows File Server.

I found nothing on this subject in Internet,
So is it impossible to sniff a LAN to capture the document, which is sent to a Spooler to be printed?

If any idea ... 

Regards,
Pejman