Hi @Anonymous,
I assume that function concatenate will work for you.
According to your description, I have made a simple test likes below:
Add a Text input control and a Label on the screen.
Set the Text property of the label with the following code:
Concatenate("APX ",TextInput1.Text," DPX")

Please check it for a reference.
Please feel free post back if you need more help.
Best regards,
Mabel