Extracting an XML config file from ZIP file and parsing it
The repeated part of your code can be extracted into a sub-function.

string InnerTextOfFirst(XmlDocument doc, string tagName)
{
  return doc.GetElementsByTagName(tagName)[0].InnerText;
}


Then use it like this:

appTitle = InnerTextOfFirst(xmlDoc, "appTitle");
appCompany = InnerTextOfFirst(xmlDoc, "appCompany");
appIconPath = InnerTextOfFirst(xmlDoc, "appIconPath");
appLargeIconPath = InnerTextOfFirst(xmlDoc, "appLargeIconPath");


This removes about a third of the inner most block.



Things to look out for:


What happens if the xml file does not have one of the tags you are expecting? It's likely that this block of code won't know the correct thing to do in this case. You should write the code so that when this happens, it is clear to the caller what the real issue is.
The C# naming convention for local variables is camelCase. While most of the variables are named correctly, the XmlNodeList variables are not.
There is a comment that refers to global variables. Having global mutable variables will make it harder to reason about how the code go into a certain state. It would be better to create a simple data class and have the code that parses the file return a new instance of that class with the parsed values.