/// <summary>
/// MBD compact method (c) 2004 Alexander Youmashev
/// !!IMPORTANT!!
/// !make sure there's no open connections
///    to your db before calling this method!
/// !!IMPORTANT!!
/// </summary>
/// <param name="connectionString">connection string to your db</param>
/// <param name="mdwfilename">FULL name
///     of an MDB file you want to compress.</param>
public static void CompactAccessDB(string connectionString, string mdwfilename)
{
    object[] oParams;

    //create an inctance of a Jet Replication Object
    object objJRO = 
      Activator.CreateInstance(Type.GetTypeFromProgID("JRO.JetEngine"));

    //filling Parameters array
    //cnahge "Jet OLEDB:Engine Type=5" to an appropriate value
    // or leave it as is if you db is JET4X format (access 2000,2002)
    //(yes, jetengine5 is for JET4X, no misprint here)
    oParams = new object[] {
        connectionString,
        "Provider=Microsoft.Jet.OLEDB.4.0;Data" + 
        " Source=C:\\tempdb.mdb;Jet OLEDB:Engine Type=5"};

    //invoke a CompactDatabase method of a JRO object
    //pass Parameters array
    objJRO.GetType().InvokeMember("CompactDatabase",
        System.Reflection.BindingFlags.InvokeMethod,
        null,
        objJRO,
        oParams);

    //database is compacted now
    //to a new file C:\\tempdb.mdw
    //let's copy it over an old one and delete it

    System.IO.File.Delete(mdwfilename);
    System.IO.File.Move("C:\\tempdb.mdb", mdwfilename);

    //clean up (just in case)
    System.Runtime.InteropServices.Marshal.ReleaseComObject(objJRO);
    objJRO=null;
} 

string connectionstring = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\data.accdb;Persist Security Info=False";

oParams = new object[] {
        connectionString,
        "Provider=Microsoft.Jet.OLEDB.4.0;Data" + 
        " Source=C:\\tempdb.mdb;Jet OLEDB:Engine Type=5"};