Hello,

we changed from Office 2003 to Office 2013.

A user who creates many documentations by using master documents informed me, that he cannot work longer by using Word 2013, because extending master documents or refreshing table of contents takes long time.

In Word 2003 it takes few seconds, in Word 2013 in takes some minutes!

How can I improve this?

BR,

The Master Documents "Feature"  in Word has long been broken. It remains broken in Word 2013 AFAIK. Read the linked article. There are alternatives. One of the easiest ways to lose tremendous amounts of work is to edit documents in Master Documents form. That you have used it this long without losing work is a minor miracle.