The photocopy of the birth act has arrived, provided by the Mairie de Paris (quite an authentic document for a fraudster!).
Pierre Athanase Marie was born on March 18, 1920, 2 am, at his parents' home, 35 rue de Lille in Paris. His parents were Pierre Plantard, 42, valet de chambre, and Amélie Raulo, 36, no profession. (follow the witnesses' names).
Additional information in the margin:
Married Anne Léa Hisler at Paris, 7th arrondissement, on December 6, 1945.
Married a second time at Paris (16th arrondissement), March 18, 1972.
I'm not allowed to upload a scan since I would need special permission from the Archives de Paris for that (this is stamped in red on the document).
We have the information on his first wife from her death act. This information matches the Geneanet profile mentioned above.
(Edited to remove name of the second Mme Plantard, who is likely living).