The rights are currently held by Bloomsbury Academic (who acquired Continuum). They have a financial interest in protecting this digital asset. While they have released e-book versions, these are typically DRM-protected (e.g., Kindle, Adobe Digital Editions) and cannot be freely shared as a simple PDF.
You might ask: Can’t I just read a Wikipedia summary of Russian philosophy? No. Here is the unique value of Copleston’s Volume 10: copleston history of philosophy volume 10 pdf