In addition, you can insert placeholders, such as floating text fields, and the values of run-time properties, such as page count, current page, and current date/time, into text objects.
The text object has the Make Fixed-Sized Text Objects Auto-fit While Editing option (Tools > Options > Workspace) selected by default. Therefore, the object automatically resizes at design time to accommodate the text you enter and the property settings you change, such as margins, borders, and font type and size.
See also 

Overview of text