The Interior Ministry said several other people were suffering from shock.
"Someone came to the office and left a package. The secretary that opened it in fact opened a parcel bomb. The parcel bomb killed her," said senior Paris lawyer Christian Charriere-Bournazel.
Paris Mayor Bertrand Delanoe said the building targeted - in the 8th district of the French capital - also houses a foundation that does research on the Holocaust. But the mayor stressed that he knew of no link between that fact and the attack.
The building also houses a law firm that Nicolas Sarkozy, now the French president, used to work with.