To have it on your PDF in correct format you have to take care in wich country your Company is located:
Settings - Companies - Your Company Address Field: Country

The Language of that country will be used for your Header and Footer of PDF-Reports.
If you have set e.g. "germany" as Adress of your company then you have to change the format of Language German:

Odoo allows changing date format on a database level for every language. The default date format is MM/DD/YYYY. Suppose you need to change the date format to DD/MM/YYYY. To do the same, perform the following steps.

1. Navigate to “Settings>Translations>Languages” Menu form Administrator account.

2. Choose the language for which you want to change the date format from the listandopenitsform view and click on edit to modify.

3. For the format, MM/DD/YYYY, the entry in date format is “%m%d%y”. To change this to DD/MM/YYYY, we can modify it to “%d%m%y” and click on save.
   https://apagen.files.wordpress.com/2013/04/3.png
   

4. You can now see any list or form view in the system to see the changes. 

its showing in views(tree view and form view..) like dd/mm/yy its working fine Thank you # ..but  in database it had stored like yy/mm/dd..because im printing a one object value in pdf at that time date has come like yy/mm/dd but i want dd/mm/yy on pdf.... problem is storing data in database.. its storing like yy/mm/dd so when we storing in database i want store like dd/mm/yy so how can i achieve this one??