It is not a problem of Photos, but of older applications like Word or Powerpoint. You can drag and drop to Mail, to Pages, Keynote.
Photos is a completely new designed application, written for the newest MacOS X version Yosemite 10.10.3. All code has been written new from scratch, using the new frameworks developed for Yosemite. But that means hat older software is not fully compatible with Photos and needs to be updated.
Consider to use iPhoto, if you need to use older applications like the current MS Office software, until compatibility updates are available for Word or Powerpoint. When installing major system upgrades older software may become incompatible or at least no longer fully supported, because required services of the operating system may have changed.
For MacOS X 10.10.3 install iPhoto 9.6.1, it is working well with Yosemite. If you did not yet update to version 9.6.1, see this user tip:
Get iPhoto 9.6.1 if you didn't update before OS... | Apple Support Communities
You cannot drag and drop from Photos to older applications that have not yet been updated to be fully compatible with Photos and MacOS X 10.10.3. You will have to wait for an update fore Word, Powerpoint, etc, to make them fully compatible.