No, client validation should not be used to validate a file field.
You should use server validation for validating a file field.
as for file manipulztions, they are intergated intyo Form Builder 2 and Universal Email.
I would like to rename the uploaded files to something like photo_001, photo_002, etc so that thw photos become anonymous, how might I do that? 
on the first page of the wizard set the option If file exists: rename new.
then on the second page, change the File Option from "[FileName]" to "photo"
this will cause the first file to be uplaoded as photo.jpg the next as photo_1.jpg, etc.
What is, and how would you use the "Default file" field displayed at Step 2 of 2 (Specify file output options) of the File Manipulation Wizard? See attachment screen shot.
the default file is the value that will be give to the Server File Name when a file is not uploaded.
see the "Adding Digital File Pro to DataAssist.." tutorial, specifically the update page section for details.
