Hi Dave,
1 ) Use CL_BCS instead of SO_NEW_DOCUMENT_ATT_SEND_API1 here example code :http://scn.sap.com/thread/3345900
2 ) If you want to use SO_NEW_DOCUMENT_ATT_SEND_API1, send PDF XSTRING data to CONTENTS_HEX and comment CONTENTS_BIN
I hope this will help