How to Edit 7.5 projects with UiPath 8
The main question when you upgrade from UiPath 7.5 to version 8 is: "Will the old processes work as expected?" The answer is "Yes". You can run or edit a workflow made with 7.5 as long as UiPath.V7.Activities package is installed.
You can find every package that you need in Manage Packages.
It is not recommended to use UI Automation activities from version 8 along with UI Automation activities from v 7.5 in the same workflow. To see the compatible activities, you can check the Compatibility option from the Activities Panel. To ensure you don't mix the activities from different versions it is best to check the "Compatibility" and uncheck the "Available" options. This way you will find in the Activities panel only the activities for UiPath 7.5 .
How to spot the difference between an activity from V7.5 and one from V8?
At first sight some of the compatibility activities seem indistinguishable from the new ones, but if you look at the properties panel you will see some differences. The name of a V7 activity starts with UiPath.Activities. By contrast, the names of the new UI Automation activities start with UiPath.Core.Activities.
Here are the properties for the Type Into activity. On the left side you have the properties of V7 "Type Into" and on the right side you have the properties for the V8 one.