This is the code:
FileInfo[] flist = d.GetFiles();
if (flist.GetLength(0) > 0)
{
foreach (FileInfo txf in flist)
{
string fn = txf.FullName +
According to the documentation, FullName field of a FileInfo object includes full path, file name and file extension (FileInfo inherits FullName from FileSystemInfo). So it is more like the code, which is in charge for creating these files, is not appending the proper extension (Assuming d is a DirectoryInfo and not other - maybe homemade - class).