the signature of CL_DOCUMENT_BCS~ADD_ATTACHMENT:
suppose we already have PDF binary source with type XSTRING, variable iv_pdf_content.
i_attachment_type: value list of attachment type could be found in value table TSOTD:
in PDF, we should use BIN
i_attachment_size: could be filled via xstrlen( iv_pdf_content )
i_att_content_hex: cl_document_bcs=>xstring_to_solix( ip_xstring = iv_pdf )
i_attachment_subject: for example test.pdf
finally the PDF attachment could be found in email box.