Zotero 7 Basic course

The links to the full text of publications can be added to the references in the URL or DOI field.
Such a link is often included when you import references from bibliographical databases.

Use the button Attachments +  to add a File, Linked File or Web Link (PDF, Word, Excel etc.) which you saved on your own PC.
The added file is also included in C:Users>U/S/E/Z-number>Zotero>storage.

From within Zotero you can also search whether a full text of a reference in your library can be found on the internet.
To achieve this you have to adjust some settings once-only  via Edit – Settings – General

• File Handling: Tick the boxes (as shown on the screenshot below)
• File Renaming: Tick the boxes (as shown on the screenshot below)
  
• Locate: Type after Base URL: https://ru.on.worldcat.org/atoztitles/link
  

Now you can have Zotero search the internet for the full text of a reference in your library.
Select reference(s) in the short title list and click right-mouse-button and select Find Full Text.
The Find Full Text screen appears and show if Full Text is succesful added as an attachment (a paperclip icon will appear).