Attaching Document in a UTL_SMTP email

I found code on here that allowed me to attach a document to an email. This worked fine but it uses COMMAND_SYS: 

PROCEDURE EMAIL_DOC(mailto_ varchar2,mailfrom_ varchar2,doc_class_ varchar2,doc_no_ varchar2,doc_rev_ varchar2,doc_sheet_ varchar2,title_ varchar2,subject_ varchar2,message_ varchar2) IS
        file_name_  VARCHAR2(2000);
        file_names_ VARCHAR2(2000);
        doc_type_   VARCHAR2(2000);
        f_          VARCHAR2(2000);
        error_msg_  VARCHAR2(32000);
        rec_ Plsqlap_Record_API.type_record_;       
        doc_ref_    VARCHAR2(32000);

        CURSOR get_doc_reference IS
            SELECT doc_object_desc
                FROM DOC_REFERENCE_OBJECT
            WHERE doc_class = doc_class_
                AND doc_no =  doc_no_;   
    BEGIN

        OPEN get_doc_reference;
        FETCH get_doc_reference INTO doc_ref_;
        IF get_doc_reference%FOUND THEN
                EDM_FILE_API.REFERENCE_EXIST(f_, doc_class_, doc_no_, doc_sheet_, doc_rev_,'VIEW');
                IF f_ = 'TRUE' THEN
                    doc_type_ := 'VIEW';
                ELSE
                    doc_type_ := 'ORIGINAL';
                END IF;

            file_name_ := EDM_FILE_API.GET_NEW_LOCAL_FILE_NAME(doc_class_, doc_no_, doc_sheet_, doc_rev_,doc_type_,'1');
            BATCH_TRANSFER_HANDLER_API.Download_From_DB(error_msg_, doc_class_, doc_no_, doc_sheet_, doc_rev_, doc_type_, 1, file_name_);
            DBMS_OUTPUT.PUT_LINE('Error: '||error_msg_);

            IF(error_msg_ is not null) THEN
                COMMAND_SYS.MAIL(
                    FROM_USER_NAME_ => mailfrom_,
                    TO_USER_NAME_ => mailto_,
                    CC_ => 'HARDCODED_EMAIL',
                    TEXT_ => message_,
                    SUBJECT_ =>subject_);

            ELSE
                COMMAND_SYS.MAIL(
                    FROM_USER_NAME_ => mailfrom_,
                    TO_USER_NAME_ => mailto_,
                    CC_ => 'HARDCODED_EMAIL',
                    TEXT_ => message_,
                    SUBJECT_ =>subject_,
                    ATTACH_ =>  file_name_ );
            END IF;

       END IF;
       CLOSE get_doc_reference;
    END EMAIL_DOC;

I would like to use UTL_SMTP instead but I can not seem to get it working for this. My main reasons for this is that I need to have the address come from different users and HTML formatted emails are preferrable for formatting.