To export your content from ReadCube Papers, simply select the references you're looking to export and then right-click. You'll see the following menu appear:
This will allow you to export your content in .bib and .ris formats. You can also select multiple references to export multiple ones at the same time.
Note: This will only export the references from your library and not the PDFs.
To export your PDFs, you will need to set your library up for file management. During this process, you will select what folder on your computer to download all the PDFs from the cloud into. You can also select a naming convention for the PDFs so they don't download as letters and numbers.
Next, you will need to sync the desktop app for offline syncing by heading to the Gear icon next to All Papers > Sync Offline.
Once selected, your PDFs will begin downloading from the cloud into the folder you designated under file management. If you have a large library it may take a few minutes to completely download your full library. Your notes and annotations will download on the PDF as well.