In case you want to make some changes on theme file of PrestaShop back office pages, here is the better way to do that instead of modifying original theme file itself.
PresataShop provide theme override mechanism for you to do that so you can keep original theme file not touched, you can copy the original file to theme override folder and then modify the copied theme file.

One back PrestaShop office pages are made up by multiple theme files, related theme files are organized into folders based on the admin page name (controller of the page).
For example, back office Orders page, the controller is AdminOrdersController.php.  The theme files are organized as following

Controller:
AdminOrdersController

Theme files folder:
YourStoreRoot/[adminfolder]/themes/default/templates/controllers/orders/

Where [adminfolder] is your store admin folder. (It is usually renamed after installation)

1. Overrride of controller theme file - for example view.tpl

Original theme file
YourStoreRoot/[adminfolder]/themes/default/templates/controllers/orders/helpers/view/view.tpl

Override theme file should be located at following - the green part must be patched.
YourStoreRoot/override/controllers/admin/templates/orders/helpers/view/view.tpl

2. Override of include theme files
In the controller theme files, sometimes you will see it includes other additional theme files like following line:   

{include file='controllers/orders/_product_line.tpl'}


In order to override included theme file, you will have to do the same thing od controller theme file.
Original theme file 
YourStoreRoot/[adminfolder]/themes/default/templates/controllers/orders/_product_line.tpl

Override theme file should be located at following - the green part must be patched.
YourStoreRoot/override/controllers/admin/templates/orders/product_line.tpl

After this, you will have to do something additional so that the override included theme file will work, you have to change the include line to use relative path as following

{include file='../../_product_line.tpl'}