Probably. As others have posted, if it's a cheapo full suspension or even a bike with front suspension, it may not be suitable for touring anyway. If it's rigid, it should be fine. If it doesn't have rack mounts on the fork and rear stays, you can also use p-clamps.
You will need slicks, new inner tubes (at least 3 inner tubes IMHO), a rear rack and a front rack or front handlebar bag to help with weight distribution. Though that's not absolutely necessary, it is a very nice thing to have and may provide more stable handling at speeds. I have a little front rack that attaches to the brake bosses, and while it can't take a heavy load, I find I can easily put my tent on it -which is really nice to even out the load. You can also take a rear rack and with a bit of mechanic ingenuity with the brackets, make it fit to the front fork.
A word of caution with the slicks: yes, some mtb rims (Sun Rhyno Lites come to mind) are wide, and not suitable for slicks down to 1.25 inches. While I don't think the manufacturer will explicitly say they aren't suitable -or you will be hard pressed to get an answer -eye ball the width of the tyre to the rim width -there should be a generous amount of "overhang" for each side of the tyre. If in doubt, don't do it. Fortunately, most mtbs don't come with Rhyno Lites or similar as standard. Secondly, a really cheap way to increase different hand positions is to include bar ends -really sensible and usable in my experience, though again, some people don't like them.
While trekking/butterfly bars are nice, I think it will be almost a necessity to also buy a new stem or quill as well -the trekking bars usually don't translate with the original stem or quill lengths.
edit: you might want to see my recent post in
https://www.cyclechat.net/
The link to converted mtbs is interesting.
My friend who wants to do LEJOG with me next year. Is asking me if he can convert his MTB into a tourer for a small fee, under £80.
Thanks