Hello everyone, 

I am new to using wincc rt. I have a very quick question.  
I have an application that is already working with wincc RT 
but I want to add some new buttons to the application so my question is: 
can I modify the .mcx file? or do I have to have the .ap file to be able to do that?

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Split from Error in creating .mcx file.

Hello MecatronicPII,

at first an general advice:
There is a post which describes which info about your system you should include in your question:
https://support.industry.siemens.com/tf//ww/en/posts/what-do-we-need-to-solve-your-problem/141582/?page=0&pageSize=10
With this information, is often easier for forum members to help you.

Now to your question:
For making changes in the Runtime, you need to have the project file (.ap). 
You must open this file and do your changes there, in TIA Portal.
The compiled Runtime file is not sufficient.

Regards,

Nzett11