In word 2016 - how to rearrange the order of the page.

What is your Office version? This feature is available only for Office 365 subscribers. For Office 2016 i.e. not the subscription version of Office 365, the button has been made available but the functionality has not been made available. Hence, the button comes up as greyed out. This is logged as known issue with Microsoft.

It is not straight forward to rearrange the pages in Word like you can do in Powerpoint. You will have to cut and paste the relevant content on a page. Movement of whole page is not possible in Word.

There are some possibilities are like if you having headings, you can move them in view > navigation pane. Similarily page / section breaks may offer flexibility. But they don't offer what you are seeking.

This is the problem in all the documents. I tried every possible thing, this thing will not come on. But my ultimate goal is to rearrange the order of page. Like move page 2 to page 8 location. 

thank you

Is this the problem with all documents or with some specific document?

I tried all the steps you sent, but it does not help. Side to Side is still grayed out. It is not that complicated to 

Try following one by one and see after every step whether it resolves the issue-

1. Sometimes, add-ins can cause problems. To determine, if add-in is a problem start your application in safe mode and see if problem has gone away.

To start in Safe Mode -

Hold CTRL key and click on application icon and don't release the CTRL key till it asks you for Safe mode confirmation.

If yes, then start application normally and disable add-ins one by one and start application again every time you disable an add-in to determine the culprit add-in.

2. Try repairing your office installation (Quick repair is good enough). Try repairing your Office installation. First try Quick Repair (takes 5 - 10 mins) , if that doesn't help then try Online Repair (Takes more than 30 mins but less than 1 hour in general)

https://support.office.com/en-us/article/Repair...

3. Login to Windows with a new user profile and see if problem is resolved.
4. Sometimes, this is caused due to application not being able to access the default printer. Close all office applications and change your default printer through Start > Devices and Printers to another printer. It may be some physical one or One Note or XPS or PDF or anything else. If this is the problem, then you will need to update your printer driver for default printer.
5. Many third party applications also cause the problem like Tuneup Utilities, Abby Finereader, Kaspersky / Avast Anti Virus etc. See if you have any of them installed. Close them one by one and see whether it helps.