Is it necessary to file original documents with the Russian Patent Office (POA, etc)?

It depends on the proceedings.

Such documents as priority documents, agreements (assignment, license, franchise), letters of consent should always be provided in original format.

As for the POA, in the majority of cases a scanned copy is sufficient. However, in some cases it is necessary to provide the original:

• upon a request from Rospatent (usually when the disposal of rights is recorded, and trademarks attorneys sign the documents on behalf of the parties)
• when appeals and oppositions are considered by the Chamber for Patent Disputes (Rospatent’s department).