Can you convert a spool file to .txt file? Yes. (Do you need to be able to recover it as a spooled file on the remote server? Or is lines of text good enough?)
Can you transfer an IFS file between IBM i servers without using FTP? Sure. SNADS, e-mail (SNDDST or MIME API), make a share available on one server and MKDIR in \QNTC on the other after which it's just a CPY or equivalent, NFS mount, SAVRST *CMD (if you have ObjectConnect installed), ...
If you convert the SPOOL file to "text" using CPYSPLF to an outfile, you can then copy that file using DDM to another system. For example, if you create your file on system A and another file on system B with the same size/definition, you can use CPYF to copy it over.
But what is your real goal? Do you want to move the SPOOL file to another system's IFS location in text format for other apps to use it, such as Excel?
If you simply want to move the original SPOOL file so people can re-print it on the other IBM i system, then you should use the SNDPRTF command in COZTOOLS or use IBM's SNDTCPSPLF command, but read the articles on SNDTCPSPLF on this site first.
If this is not some reoccuring event (or even if it is), you can copy/paste them with inavigator, if inav has access to both machines.