In my project, I have a requirement to place all the files attached in attachment control to the SharePoint document library below is the code to achieve the same.

XPathNavigator FormNav = MainDataSource.CreateNavigator();
XPathNavigator node = FormNav .SelectSingleNode("//my:document", NamespaceManager);
string attachmentValue = string.Empty;
if (node != null && !String.IsNullOrEmpty(node.Value))
{
attachmentValue = node.Value;
// Write your own decoder class.
InfoPathAttachmentDecoder decoder=new InfoPathAttachmentDecoder(attachmentValue);
string fileName = decoder.Filename;
byte[] data = decoder.DecodedAttachment;
// Add the file to a document library
using (SPSite site = new SPSite("http://mysite"))
{
using (SPWeb web = site.OpenWeb())
{
web.AllowUnsafeUpdates = true;
SPFolder Lib = web.Folders["Shared Documents"];
Lib.Files.Add(fileName, data);
web.AllowUnsafeUpdates = false;
web.Close();
}
site.Close();
}
}