Open the document by clicking on its title
Click the second tab 'Tags & Details'
Type your tag
Your new tag is now displayed on this page.
You can add several tags.
Open the second filter untitled 'Tags'
You see the tags by frequency and the number of tagged documents
You can search using the search bar
You can select one or multiple tags
To find all your documents tagged with specific tag(s):
Type the tag(s) in the main search bar
Select 'Tags' in the field dropdown menu
Click 'Search' or press 'Enter'
The results are all the documents tagged with the tag(s) you typed in the search bar.
To find all your tagged documents, whatever the tags:
Type nothing in the search bar
Select 'Tags' in the field selector
The results are all the tagged documents.
Click the cross at the end of the tag that you want to delete.