I have several bikes. I noticed that 90% of times I go on road so I got myself a road bike. But, can I use it for off road? Nothing extreme maybe some dirt roads or with small stones or poorly maintained roads. There is a really small amount of rains here so mud it is not a danger. The idea is that I can lend it to a friend to make some soft off road routes or use it myself and lend a more off road bike.
There's a whole sport - cyclocross - that involves riding road bikes off road. Typically the gearing is a little lower than a stock road bike, and these days a lot of them have disk brakes. Most will take fairly wide tyres, 38mm is not out of the question.
For riding a stock road bike off road, I'd look mostly at tyres. If you can find some that will clear your frame that have a bit of tread that will help a lot. Puncture resistance may also be worth while, you're more likely to find thorns off road. I would also experiment with lower tyre pressures, as that may improve traction.
Other than that, I'd just ride and see what happens.
In poor country, there is not "nice pave road" and "special cross country bicycle", cyclist just use their bicycle as daily utility tools and no complain. As long as you are not playing extreme (e.g. play the downhill) .
If you are worry about comfort, punctured, then change to wider tyre, use puncture resistant tyre, good double wall wheel rims. All the extra cost actually will pay themselves in long term. Ride carefully will avoid damaging your rims.
Put some reasonably durable 25c or 28c tyres on and you should be fine. Also think of gearing ... trails can get steeper than road and traction can degrade quite a bit, requiring shorter gear ratios.
Certainly can !
I did a camping tour with a road bike - with a bike rack - and tent/sleeping bag, etc - we did gravel roads - just standard road bike tyres. Next time, I might get more durable, or grippy tyres. We did 4 days of 80km (330km in total)
Road bikes can definitely handle offroad conditions. A good example is the Paris-Roubaix race. In this race there are a lot of roads built out of old cobble stones. Often riders will ride of the side of the cobbled sections which is basically hard packed dirt (or mud, depending on the weather). There are also sections in the mountains on the Giro D'Italia that use gravel roads. And if you're still worried about what your road bike can do, check out this video.
The thing that makes road bikes unsuitable off good pavement is their narrow, high pressure tires. The gearing and seating position may not be ideal, but they are not killers. For a short stretch, you just need to get through it. Hard packed dirt is no problem unless there are ruts along the direction of travel that cause control problems. A thin layer of sand or gravel over a hard surface is also not a problem as long as you corner gently. The problem comes if you have a soft surface that cannot support your tire pressure or sharp rocks that puncture a thin road tire. These can quickly ruin your day. Long stretches of the other surfaces may make you wish you had a different bike, but tell your friend that beggars can't be choosers and pick a route that doesn't have too much of them.