This gist show a solution that I've figured out to open all documents links on model object detail page of Django's admin on a new tab.

pop_up_admin_file_widget.py

class NewTabAdminFileWidget(AdminFileWidget):
    """
    This widget is an extensions from AdminFileWidget which is used with all
    ImageFields and FileFields at admin forms. This widget follows the api defined
    by django.forms.widgets.ClearableFileInput widget.
    """

    def __init__(self, *args, **kwargs):
        super(NewTabAdminFileWidget, self).__init__(*args, **kwargs)
        template_with_initial_new_tab = (
            '%(initial_text)s: <a href="%(initial_url)s" target="_blank">%(initial)s</a> '
            '%(clear_template)s<br />%(input_text)s: %(input)s'
        )
        self.template_with_initial = ('<p class="file-upload">%s</p>' % template_with_initial_new_tab)


class YourModelAdminForm(forms.ModelForm):
    
    def __init__(self, *args, **kwargs):
        """
        Changes widget of FileFields to open documents on new tab
        """
        super(YourModelrAdminForm, self).__init__(*args, **kwargs)

        for field_name, field in self.fields.items():
            if isinstance(field, forms.FileField):
                field.widget = NewTabAdminFileWidget()

    class Meta:
        model = YourModel
        exclude = []

Is there a particular reason to use string interpolation? (line 14)