Civil record copies from the local registrars' office (bureau de l'état civil) from your ancestor's town...however as civil registration only started in 1792.
French Parish registers date back to as early as 1334, though the majority of surviving records date from the mid-1600's.The majority of church records prior to 1792 are held by the Archives Départementales, though a few small parish churches still retain these old registers. Libraries in larger towns and cities may hold duplicate copies of these archives.
Census records in France date back to 1772 but prior to 1836 ( when they were taken every 5 years) usually only noted numbers of people per household, though sometimes they would include the head of household as well.
In France, tombstones with legible inscriptions can be found from as early as the 18th century.
Military records are held by the Army and Navy Historical Services in Vincennes, France and records survive from as early as the 17th century.
Notarial records are an important sources of genealogical information in France. These are documents prepared by notaries which can include such records as marriage settlements, wills, inventories, guardianship agreements, and property transfers (other land and court records are held in the National Archives (Archives nationales), mairies, or Departmental archives. They include some of the oldest available records in France, with some dating all the way back to the 1300s.
Now I have been tracing family history for many years...and sorry but I doubt you have a recorded verified paper trail back to France to 0900AD, as if the people who look after a Nations records don't have records of that date...how come you do?
Now I know the French are a clever nation, however people going back only 150 years ( and thats only back to 1860) all the people didn't read and write, so few records of events were taken and France is better than many European countries for records.
Basically you would be wasting your time visiting France other than to see the Country as the 'records' you seek don't exist...you would be better, verifying what you already have, one wrong person in your family history means you are not tracing your family but someone else's, to make sure you do have a family tree which is your family tree and not some copied information from the internet with no references to real records and even if you have got reference numbers, have you checked them to see if they are correct?
For each person, each FACT about them you need THREE PRIMARY document/record sources before you believe that person is the correct person and you are better to have a real family tree back to 1850 that you know is genuine as you have all the references and copies of documents than some massive 'tree' of copied information, not referenced and really no idea if it is correct or not