AutoCAD .NET :: Lock Document Without Open It?

I'm trying to update a xref path of a autocad document without open it. I've tried something like this to access the database of a document

using (Database db = new Database(true, false))
{
db.ReadDwgFile(fullpath, System.IO.FileShare.ReadWrite, false, "");
// rest of the code ....
}

In order to do that the readdwgfile the document must be locked right? Because i'm going to modify blocks of the document. So how can I lock a document without open it?