Just drag them from the folder on your computer to the Zotero window. But note that moving forward, the best way to add items to your library is using the Save to Zotero button in your web browser.
Not sure exactly what you are asking. But I'll try...
Assuming that you start with say a Journal article (whatever really...)
1. You select that item in the middle list. 2. Right mouse button bring up a dialog box for which one of the options is "Add Attachments >" 3. Now there are three options (1) "Attach Link to URL..." Brings up a dialog box with two fields. One for URL and other for a name. (2) "Attach Stored Copy of File..." Brings up a dialog box which allows you to select a file from your PC files. In this case the file itself is copied into a subdirectory of the Zotero directory "storage" and becomes a part of the Zotero database which can be synced with the cloud application. (3) "Attach Link to File..." Brings up a dialog box which allows you to select a file from your PC files. In this case just the filename is linked within the Zotero database. No copy of the file is made. The pdf file won't be uploaded to the cloud when the PC/Cloud versions are synced.
Just tested and dragging & dropping onto an item within the PC version creates a "Stored Copy" of the file. So the file itself is copied into the Zotero database. (That should really be made clear on webpage that bwiernik supplied...)
Attaching a file (i.e. storing a copy) is the default for any file behavior in Zotero. It's also the only way to attach files that has file sync work out of the box -- in other words, it's what anyone who isn't sure what they want/need should be using.
Upgrade Storage
Just drag them from the folder on your computer to the Zotero window. But note that moving forward, the best way to add items to your library is using the Save to Zotero button in your web browser.
Assuming that you start with say a Journal article (whatever really...)
1. You select that item in the middle list.
2. Right mouse button bring up a dialog box for which one of the options is "Add Attachments >"
3. Now there are three options
(1) "Attach Link to URL..."
Brings up a dialog box with two fields. One for URL and other for a name.
(2) "Attach Stored Copy of File..."
Brings up a dialog box which allows you to select a file from your
PC files. In this case the file itself is copied into a subdirectory of the
Zotero directory "storage" and becomes a part of the Zotero database which
can be synced with the cloud application.
(3) "Attach Link to File..."
Brings up a dialog box which allows you to select a file from your
PC files. In this case just the filename is linked within the Zotero
database. No copy of the file is made. The pdf file won't be uploaded
to the cloud when the PC/Cloud versions are synced.
Does that help or did I confuse you more?