Technically, you can only archive and restore campaigns. In order to effectively pause or resume campaigns, you need to pause or resume all the ad groups within the campaign.
Pause a campaign
1. Go to the campaign you need to pause, scroll down and select all ad groups.
2. Click on the Actions button and select Pause.
Resume a campaign
1. Go to the campaign you want to resume, scroll down and select all ad groups.
2. Click on the Actions button and select Enable.
Archive a campaign
Archiving a campaign is only possible after these three conditions are met:
All the ad groups within the campaign are paused,
The campaign has been inactive for three days,
There is no available budget left on the campaign.
1. Go to the campaign's Settings.
2. Click Archive Campaign at the very bottom.
Restore a campaign
1. Select the date range in which the campaign ran. This will pull up the campaign data in Zemanta tables.
2. Click on the Filter button, check Show archived items, and click Apply filter.
3. Restore the campaign by clicking on the icon next to it, as shown in the image below. Alternatively, you can check the box next to the campaign, go to Actions and select Restore.
Keep in mind that by restoring a campaign, you only unarchive it, but it is still paused. Follow the instructions in the segment Resume a campaign above to get it running again.