Is remote printing secure?

Yes, there can be logs. No, previously printed documents are not saved in a way
that they could be re-printed or viewed again later.

However (isn’t there’s always a “however”?), depending on your level of
concern, printing may not be as secure as we casually assume.

First the log.

The computer that a printer is connected to can be configured to log all
printing events to the System log. You can use Window’s Event Viewer on that
machine to see what documents have been printed, and by what user.

For example, I just printed a test document, and in the event log I found
this:

That log can contain the name of your document, as well as the computer name
and user name of the account printing it. If the printer is shared, of course
the computer name would be the name of the remote computer accessing the shared
printer.

So, yes, while logs aren’t guaranteed to exist (mine was off by default),
they certainly can be enabled, and can contain some interesting
information.

Next we need to examine exactly how printing works.

When you print a document it invokes something called the “print spooler”.
Rather than printing directly to the printer, the information that would be
sent to the printer is actually written to (or “spooled”) to disk, and sent on
from there. Your application writes the printed document to the print spooler
where it’s placed in the queue of documents waiting to be printed. As prior
documents finish printing yours moves ahead in the list, and finally prints
when its turn comes.

If the printer is remote – meaning that you’re printing on machine A to a
printer connected to and shared by machine B, then your document’s print data
is written to the spooler file on machine B.

Regardless of where the spooled file lives, once your document has been
printed, that file is deleted. There’s no record of its content kept, and
there’s no way to simply say “print it again”.

Or is there?

This is where judicious paranoia might set in.

We all know by now that files aren’t really deleted, the disk space they
used is simply marked as “available to be overwritten”. Until that disk space
is overwritten – you guessed it – the data could be
recovered. It wouldn’t be easy, and on a busy system it might not even be
likely, but there is a possibility.

(Note that I’m talking about printers “shared” through another Windows
computer. Printers attached directly to a network may, or may not, contain a
log, and may, or may not, spool the documents to internal storage in a way that
might be recovered later. It all depends on their configuration and
abilities.)

So, what can you do?

Nothing, really. When you send data to another computer, any other computer,
you’re ultimately entrusting the owner of that computer with the possibility of
full access to your data and printing to a shared printer is no different.

This is one case where even encryption won’t help; your printed document
still needs to be decrypted on the remote computer in order to be
printed.

If you really need to keep that data super secure and avoid even
the slimmest chance of recovery by others, then the only real approach would be
to print it only on a computer that you control. (And consider securely wiping
the disk’s free space when you’re done, just in case.)