What a looong title 
The Problem is that reusing code for sending email with attachment from a sap non-unicode to a sap unicode system the att file (in my case was a .pdf) results unreadable, using the function SO_NEW_DOCUMENT_ATT_SEND_API1 or SO_DOCUMENT_SEND_API1 .
A typical call of the function is:
CALL FUNCTION ‘SO_DOCUMENT_SEND_API1′
EXPORTING
DOCUMENT_DATA = DOCUMENT_DATA
PUT_IN_OUTBOX = PUT_IN_OUTBOX
SENDER_ADDRESS = INVOICE_SENDER
SENDER_ADDRESS_TYPE = ADDR_TYPE
IMPORTING
SENT_TO_ALL = SENT_TO_ALL
NEW_OBJECT_ID = NEW_OBJECT_ID
SENDER_ID = SENDER_ID
TABLES
PACKING_LIST = PACKING_LIST
OBJECT_HEADER = OBJECT_HEADER
CONTENTS_BIN = CONTENTS_BIN
CONTENTS_TXT = CONTENTS_TXT
OBJECT_PARA = OBJECT_PARA
OBJECT_PARB = OBJECT_PARB
RECEIVERS = RECEIVERS
EXCEPTIONS…
And the PACKING_LIST-DOC_SIZE is usually valorized as:
PACKING_LIST-DOC_SIZE = TAB_LINES * 255.
But the right code that solve the Problem is:
PACKING_LIST-DOC_SIZE = TAB_LINES * 255 * 2.
Due to the change data representation. Helpful docs on Sap and unicode here.
Please feel free to comment 
