The file is correct. I noticed many files have that problem, it's not because files are not original, but something unavoidable. Rootsh deb is not one of them.

Put that deb files (with all their dependencies) on internal 27 GB drive .Now install "rootsh" (it's in extras repository). Open x terminal and type "sudo gainroot". Point to that location using "cd" command (example "cd MyDocs") Type "dpkg -i *.deb". If it says problem about dependencies, then install one by one, first one that doesnt depend on anything... Just type start of file name instead of "*.deb", you do not have to type full file name, it is difficult, but make sure there are no similar file names, whatever. You know what I mean. It's simply using * symbol.

Or simply install while online using App. manager, or download all repositories and connect to any wifi and that access point will stay and you will be able to somehow connect to it even when it is not available around anymore. This fake connection is needed for app. manager to be able to use offline repositories.