Let me grab my crystal ball and guess that by "DRM" you mean detecting
whether the document has been altered or not, given that keeping people from
copying a document is impossible.
In that case, you don't need a Windows program. LibreOffice, which does
either everything MS Office can do or close to it, can sign documents for you.
LibreOffice runs natively on Linux, Mac, and Windows, that is, without WINE or
VirtualBox or any compatibility aids.
It uses asymmetrical encryption (that's where one key decrypts and one key
encrypts) so that only you, the sole bearer of the secret private key, can
create a signature for a document that when someone takes the public key, which
you bundle with the document and release to a certificate authority and is
mathmatically related to the private key, and uses that with a hash of the
document, the signature is computed. If it matches the signature bundled with
the document, then it's an original. If not, then the document has been
altered.
One could verify that that really is your public key by going to the certificate
authority with whom you registered that public key with your name.
I think the way it works is a hash is made of the document, then you encrypt
that hash with your private key and bundle the encrypted hash with the document.
You also bundle in the public key and your name. Then someone else who obtains
the document can calculate the hash, decrypt the encrypted hash with the
supplied public key, and see if the hashes match. If anyone alters the document,
the hashes won't match. If someone replaces the encrypted hash and public
key so that the hashes will match for the altered document, by going to the
certificate authority one could see that that public key is not registered with
who the author is supposed to be.
Cheers,
Jake