You can link your Dropbox documents to any record in Vtiger. Select the modules within which you want the Dropbox widget to appear. Then simply click the Dropbox widget on any Vtiger record, use the Dropbox search pop up to find the particular document you need and click to link it to Vtiger.
Additionally, you can sync your Dropbox folder system into Vtiger. As long as your folder name in Dropbox matches an organization name in Vtiger, all the documents in that Drive folder will be created under that Vtiger organization. As documents are added to your Dropbox, they sync to Vtiger as well. Although the syncing happens automatically, it can be performed manually when needed as well.
The best part about this integration is that the app links to the Dropbox document and not the actual document which is perfect because documents are better stored in a centralized place.