I purchased and installed your plugin on Joomla 3.6.5 + VirtueMart 3.0.16.
Immediately the site is broken with errors:
Notice: Use of undefined constant VMPATH_ADMIN - assumed 'VMPATH_ADMIN' in /plugins/system/virtuemart_order_backend_edit/virtuemart_order_backend_edit.php on line 23
Notice: Use of undefined constant DS - assumed 'DS' in /plugins/system/virtuemart_order_backend_edit/virtuemart_order_backend_edit.php on line 23
Warning: require(VMPATH_ADMINDShelpersDSvmmodel.php): failed to open stream: No such file or directory in /plugins/system/virtuemart_order_backend_edit/virtuemart_order_backend_edit.php on line 23
Fatal error: require(): Failed opening required 'VMPATH_ADMINDShelpersDSvmmodel.php' (include_path='.:/usr/share/php') in /plugins/system/virtuemart_order_backend_edit/virtuemart_order_backend_edit.php on line 23
First of all, I suggest that the plugin is NOT enabled by default during install.
Then, the 'DS' constant is long gone from Joomla and you should not use it.
Finally, 'VMPATH_ADMIN' is not defined unless you're in a VirtueMart page so this plugin will break all other pages.
Anyway, after manually editing the code to fix the issues, I edited an order from backend and don't see any button to edit the order.
I kindly ask you to support me in making this purchased extension work as expected.