You should add a "copy file" one the Files/More list down menu (see attached file).
We're excited to announce we have added the feature Copy Files to the right-hand menu. Simply select a single or group of PDFs to copy to your clipboard and paste them in another folder or program.
Please note, this currently works in the desktop app only and needs to have the PDFs downloaded from the cloud first. You can copy as many files as your computer storage will allow for the clipboard.