Every mongoengine field can be deep copied, except for file fields.

file-field-fail.py

from copy import deepcopy
from mongoengine import *
from pymongo import Connection

class A(Document):
    binary_field = BinaryField()
    boolean_field = BooleanField()
    date_time_field = DateTimeField()
    decimal_field = DecimalField()
    dict_field = DictField()
    email_field = EmailField()
    embedded_document_field = EmbeddedDocumentField(EmbeddedDocument)
    file_file = FileField()
    float_field = FloatField()
    generic_reference_field = GenericReferenceField()
    geo_point_field = GeoPointField()
    int_field = IntField()
    list_field = ListField(boolean_field)
    object_id_field = ObjectIdField()
    reference_field = ReferenceField(Document)
    sorted_list_field = SortedListField(boolean_field)
    string_field = StringField()
    url_field = URLField()

db = 'tmp-deepcopy'
Connection().drop_database(db)
connect(db)
a = A() 
a.save()

for field in sorted(a._fields):
    try:
        print field, a[field], deepcopy(a[field])
    except TypeError as e:
        print 'FAILED'
        print '\t', e

output.txt

binary_field None None
boolean_field None None
date_time_field None None
decimal_field None None
dict_field {} {}
email_field None None
embedded_document_field None None
file_file <mongoengine.fields.GridFSProxy object at 0x9930e2c> FAILED
	'Collection' object is not callable. If you meant to call the '__deepcopy__' method on a 'Collection' object it is failing because no such method exists.
float_field None None
generic_reference_field None None
geo_point_field None None
id 4d8d039e8b61460f65000000 4d8d039e8b61460f65000000
int_field None None
list_field [] []
object_id_field None None
reference_field None None
sorted_list_field [] []
string_field None None
url_field None None