RadComboBox has a built-in functionality of navigation when the PageUp/PageDown key gets pressed. n order to achieve a similar behavior for RadAutoCompleteBox as well you need to implement if from scratch. For that purpose the PreviewKeyDown event of the AutoCompleteBox needs to be handled. Inside it you need to check if the key is PageUp/PageDown and if so to navigate to the desired index of the ListBox placed inside the Popup part of RadAutoCompleteBox.
We have created a sample project that demonstrates that approach and you could run and evaluate it.
Hope this helps.
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