You can use a simple workflow to accomplish this. The workflow event would be SIH and the attachment of the workflow would be pointing to the pdf created in your script. You can check off that the workflow can be edited, hence it would open the workflow screen for the user to edit the email body and the recipients.    

Hello, thank you for your answer !

It seems to work pretty well.

Is there a way to send multiple file through a single workflow ? I added my invoice's pdf in Attached document  field (D:\Myserver\invoices\num.pdf" ) but I can't manage to find how to add a second attachment

Thanks

You can use an entry point to AWRKMEL using the EMAIL Action and set the EXP_MAIL variable to whatever email you want the sender to be. Years ago, I added a field to the workflow rules where we can specify who the sender should be for that workflow. Then in the entry point I assign to EXP_MAIL the value of that field, if it’s blank then we don’t do anything.  

In email I saw you had a question regarding sender here I see your question is regarding multiple attachments. Did you delete the previous question?
Regarding this question I think the you can use a semicolon.

Thanks for your answer, indeed I deleted my question about sender because it was a mistake on my part and there was actually no problem.

Regarding the semicolon, I did try this but I get the following message:

Incorrect Expression
Illegal Character

here is my field:

"D:\MYCOMPANY\tmp\"+"Invoice_"+[M:SIH0]NUM+".pdf";"D:\MYCOMPANY\test.txt"

Found the solution, here is the right way to do it:

"D:\MYCOMPANY\tmp\"+"Invoice_"+[M:SIH0]NUM+".pdf"+";"+"D:\MYCOMPANY\test.txt"

So to put it in a nutshell,

1) SPESIH: When an invoice is validated, the report is printed in D:\MYCOMPANY\tmp\[M:SIH0]NUM.pdf

(AVANTBOUT is used)

2) Worflow is called, it retrieve the PDF by "reconstructing" the file name (see the attachment field above)

I bet there must be an easier / lighter way to retrieve the pdf ? but for now it's the best I can come up with