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You can allow users to upload one file directly through the form, by adding the parameter uploadable to that field's declaration in the form definition.
You can also set the default filename of the uploaded files, by setting the "upload filename=" parameter in the field definition.
The value of this parameter can also include the variable "<page name>", which gets substituted with the name of the page being added or edited. So adding to the field definition the parameter "default filename=Image for <page name>", for instance, for a page called "Abc", would set the default name of any uploaded file to "Image for Abc".