TL;DR
You can sign quotes and contracts in the name of the company in formation before registration: the company will take them over once registered, provided they are listed in the articles of association or approved afterwards. Invoices, however, must show the SIREN number and the RCS registration: issue them after registration. 
Service-public
In practice
- Write on the quote: "[Name], company in formation".
- List the acts already carried out in the schedule attached to the articles of association, or have them approved after registration.
- Invoice as soon as the SIREN number has been assigned and registration is complete. Service-public
Client in a hurry?
Filing a complete application quickly is the only lever you have: see what can delay a registration.
Written by Razvan Toma, founder of LegalRapide. How we check our figures · LinkedIn