Send mail with attachment

I'm trying to send a email with attached file using the sp_send_dbmail store procedure (SQL Server 2005). The file is stored into a field of a data base table.

I succeed to send the mail with the attached file, the recipient correctly receives it (and the attached file) but
doesn't succeed in opening the file: for example if the file is a .doc the Word application doesn't read it.

In order to retrieve the content of the attached file I set the @query parameter of the sp_send_dbmail store procedure
with 'SELECT Data FROM AttachmentData WHERE AttachmentId = 78'. The type of the field 'Data' is varbinary(max).
The values of the other parameters are:

@profile_name = @MyProfileName,
@recipients = @To,
@copy_recipients = @Cc,
@subject = @Subj,
@body = @Content,
@query = @selectAtt,
@query_result_header = 0,
@attach_query_result_as_file = 1,
@query_attachment_filename = @MyFileName,
@exclude_query_output = 1,
@query_no_truncate = 1,



If the file to attach is a txt file and the @query parameter is set with 'SELECT CAST(Data AS varchar(MAX)) FROM TEST_ATTACH.dbo.AttachmentData WHERE AttachmentId = 56' the mail recipient will be able to open the file.
For the other file tipe (.gif, .doc, .pdf ecc) I try to modify the @query parameter in order to
cast to the varbinary type but it doesn't work: the recipient is not able to open the attached file.

Can help me?

Have a Nice day!
Thanks Much.