contentControlInsertOoxml.js

// Run a batch operation against the Word object model.
Word.run(function (context) {
    
    // Create a proxy object for the content controls collection.
    var contentControls = context.document.contentControls;
    
    // Queue a command to load the id property for all of the content controls. 
    context.load(contentControls, 'id');
     
    // Synchronize the document state by executing the queued-up commands, 
    // and return a promise to indicate task completion.
    return context.sync().then(function () {
        if (contentControls.items.length === 0) {
            console.log('No content control found.');
        }
        else {
            // Queue a command to put OOXML into the contents of the first content control.
            contentControls.items[0].insertOoxml("<w:p xmlns:w='http://schemas.microsoft.com/office/word/2003/wordml'><w:r><w:rPr><w:b/><w:b-cs/><w:color w:val='FF0000'/><w:sz w:val='28'/><w:sz-cs w:val='28'/></w:rPr><w:t>Hello world (this should be bold, red, size 14).</w:t></w:r></w:p>", "End");
        
            // Synchronize the document state by executing the queued-up commands, 
            // and return a promise to indicate task completion.
            return context.sync()
                .then(function () {
                    console.log('Inserted OOXML in the first content control.');
            });
        }
    });  
})
.catch(function (error) {
    console.log('Error: ' + JSON.stringify(error));
    if (error instanceof OfficeExtension.Error) {
        console.log('Debug info: ' + JSON.stringify(error.debugInfo));
    }
});