How do I distinguish a file or a folder in a drag and drop event in c#?

if(Directory.Exists(path))
  // then it is a directory
else
  // then it is a file

Given the path as a string, you can use System.IO.File.GetAttributes(string path) to get the FileAttributes enum, and then check if the FileAttributes.Directory flag is set.

To check for a folder in .NET versions prior to .NET 4.0 you should do:

FileAttributes attr = File.GetAttributes(path);
bool isFolder = (attr & FileAttributes.Directory) == FileAttributes.Directory;

In newer versions you can use the HasFlag method to get the same result:

bool isFolder = File.GetAttributes(path).HasFlag(FileAttributes.Directory);

Note also that FileAttributes can provide various other flags about the file/folder, such as:

• FileAttributes.Directory: path represents a folder
• FileAttributes.Hidden: file is hidden
• FileAttributes.Compressed: file is compressed
• FileAttributes.ReadOnly: file is read-only
• FileAttributes.NotContentIndexed: excluded from indexing

etc.