DocumentFormat.OpenXml in Ubuntu server
just put the binaries you need alongside your application executable.
for the binaries, you can build it yourself:https://github.com/OfficeDev/Open-XML-SDK
or download from below and just extract the binaries using Universal Extractor or installing it and finding them.
2.0: https://www.microsoft.com/en-us/download/details.aspx?id=5124
2.5: https://www.microsoft.com/en-us/download/details.aspx?id=30425