I suppose you've meant "but with GetFiles" (not ListDirectory).

Anyway, see FAQ:
https://winscp.net/eng/docs/faq_script_non_recursive

foreach (RemoteFileInfo fileInfo in directory.Files)
{
if (!fileInfo.IsDirectory)
{
session.GetFiles(remoteFTPDirectory + fileInfo.Name, localPath + fileInfo.Name, false, transferOptions).Check();
}
}

Unless somebody has a better idea.

I have a process where I download every existing file in a directory. Say I have:

/readme.txt
/Pub

I only want readme.txt but with ListDirectory I get everything in Pub as well. Is there a way to prevent this drill down behavior?