You can send a scanned invoice if your client accepts the "paperless" e-invoicing mode. 

If the e-invoicing mode is "audit trail" or "signed PDF" type, the PDF document must not be scanned but generated from your billing or office tool (this is called a text PDF). 

If the PDF is not compliant, it will be rejected with the reason "Document not eligible" and you will be notified. Rejected documents can be viewed in the "Rejected invoice" list on the portal.