In Confluence 7.3.0 and higher, it is possible to enable the Edit in Office feature through the UI by following these steps:

1. Heading to General Configuration > Office Connector 
2. Setting the Enable Edit in Office for all users (this will disable the Companion app) option. 

However, the Edit in Office option will only be visible through

1. The Attachment List page 
   • 
2. Through the Office Macros.
   • Office Word Macro
   • Office Excel Macro
   • Office PowerPoint Macro

In previous Confluence versions, when the Edit in Office feature was available or enabled, the feature can be accessible in the Preview mode of an attachment. This is no longer the case with the new implementation of Edit in Office, as the Edit button is not visible in this mode in all browsers.

The Edit option is not visible in specific browser

Confluence 7.3.0
In IE: (The Edit option is visible)

In Chrome and Firefox, the Edit option is not visible:

Confluence 6.13.10
Only visible in Firefox

Confluence 7.4.0
Not visible in Chrome, Firefox or Edge