To pass input from a local file to ssh, you should use input redirection like this:
ssh user@server < abc.txt
Are you sure the _ must be really a single character? In that case this is possible if x is configured in ~/.ssh/config as an alias to some user@host:
ssh x < abc.txt
I cannot answer Q2 because I don't really understand it. I suppose Remote.txt is on the remote.
As per the second question, I suppose Remote.txt is a file on the remote side, in which case the command should be of the form:
ssh user@server "bash < Remote.txt"
..but this does not fit the problem description with _ _ _ and of course to remove the trailing tabs some more would be necessary like:
ssh user@server "bash < <(sed -e 's/^[ ]*//' Remote.txt)"
I hope this helps anyway.