We do something similar:
We read the signatures from the folder (according to office version, language used in office, etc.) from this folder:
"C:\Users\..your user name ...\AppData\Roaming\Microsoft\Signatures" (for Spanish Office it would end on "....\firmas" )"
When you have created previously a signature with / in Outlook, it has been saved in that folder with different formats:
- txt
- html
- rtf
1) We read the .RTF file of the chosen signature from disk from previously mentioned folder (not sure how to know which one is the DEFAULT, but must be in the registry I guess, we simply save the last one used as default in a table).
2) Then paste that contents of the file at the end of an email that a user is writing in an RTE control.
3) Then do a SaveDocument with Html format, something like "rte_notedet.SaveDocument( ls_tempFileName, FileTypeHTML!, EncodingAnsi!)"
4) Read that html from disk and use it as the Body for the email we finally send.