dear sir, you need to inherit account.view_move_form and make you change like the folowing:

locate the field partner_id in your xpath with position replace 
then add the fowloing two fields:

              1-"partner_id" widget="res_partner_many2one" nolabel="1" context="{'res_partner_search_mode': (context.get('default_move_type', 'entry') in ('out_invoice', 'out_refund', 'out_receipt') and 'customer') or (context.get('default_move_type', 'entry') in ('in_invoice', 'in_refund', 'in_receipt') and 'supplier') or False, 'show_address': 1, 'default_is_company': True, 'show_vat': True}" options="{"always_reload": True, "no_quick_create": True}" attrs="{'invisible': [('move_type', 'not in', ('in_invoice', 'in_refund',  'in_receipt'))]}"/>

2-partner_code" attrs="{'invisible': [('move_type', 'in', ('in_invoice', 'in_refund',  'in_receipt'))]}"



  and close xpth

          if you want to restrict some users : you can change groups attributes

Hello Haseeb
You can follow below steps to allow only particular user to show customer.
1) You need create new field customer_code for invoice which is relatable to customer code.
now you can show this field in invoice to all users.
2) Now for showing customer only to particular user you can directly create one group and then assign that group to partner_id(customer) on invoice.
3)Now assign that group to users which you want to allow to show customer on invoice.

Thanks.