In most cases, Zotero will automatically save the full text of an article when you save the reference using the Zotero Connector. However, if you have created the reference manually, you can attach the full text yourself.
1. Ensure that the full text file is saved to your computer.
2. Select the relevant reference in your Zotero library.
3. Click the paper clip icon in the toolbar above your reference list, then choose "Attach Stored Copy of File."
4. Navigate to the file and click Open.
Zotero will attach the full text to the reference and place a copy in the Zotero folder. You can delete the copy in your downloads folder.
Be sure to sync your Zotero account before closing to ensure the full text is saved to your account.
Zotero is free and open source. It is run by a nonprofit who does not mine your data. Learn more about why Zotero is awesome here: https://www.zotero.org/why