In this case the Style property returns an object. Try this to get the style of the text you selected:
#include <Word.au3>
Local $oWord = _Word_Create()
If @error <> 0 Then Exit MsgBox(16, "Word UDF: _Word_DocOpen Example", "Error creating a new Word application object." & @CRLF & "@error = " & @error & ", @extended = " & @extended)
Local $sDocument = "Test_Format.doc"
Local $oDoc = _Word_DocOpen($oWord, $sDocument, Default, Default, True)
If @error <> 0 Then Exit MsgBox(16, "Word UDF: _Word_DocOpen Example 1", "Error opening 'Test.doc'." & @CRLF & "@error = " & @error & ", @extended = " & @extended)
MsgBox(64, "Word UDF: _Word_DocOpen Example 1", "Select range!")
Local $oRange = _Word_DocRangeSet($oDoc, 0)
ConsoleWrite("Selected Text: " & $oRange.Text & @LF)
ConsoleWrite("Style of Selected Text: " & $oRange.Style.NameLocal & @LF)