Make a copy of the “Storage” file of your Zotero library onto your desktop for a backup in case anything weird happens after moving your attachment files to Dropbox.
***Please note this involves looking in your data directory, so please be careful here.
This “Storage” file is inside of your “Zotero Library” folder. Here is how to find it:
1) Find your Zotero Library location by going to Zotero>Preferences:
2) A popup window will open. Select the Advanced icon, then in the options just below, select Files and Folders, then click on where it says: Show Data Directory:
3) Open the Zotero folder that you are brought to:
4) Find the folder inside of it called “Storage”
5) Right click and make a copy of the "storage" folder to save to your desktop.
You probably won’t need it.
6) Paste the copy onto your desktop:
7) Rename the copied file (now on your desktop) to Zotero Storage Backup: