Hi,You try this:
<field name="file_type" position="attributes">
<attribute name="attrs">{'readonly': ['|',('file_type',in',['trademark_user','company_user']]}</attribute>
then follow the instructions:
1.Log in into any one of the user(trademark_user,or company_user or all user)
2.Enable the developer mode in openerp
3.choose any one of the type in the field "file_type"
4.Then in the debug view menu,there is a menu called " Set Default"
5.you must select your field in the "Default:" field by using the drop-down list
6.Below the "Default:" field, You can see two options called "only you" and "All users".if you select "only you" option the field value used for the customer you logged in.if "All users" means it should be used for all the users.
7.save the value. 8.Log out the current user and log in the next user and continue the above process.
whenever you sets a default value in this method,it stores in the Settings/Technical.Actions/User-defined defaults with the field name and model name.you can delete it there .
hope it is useful for you