Where did you read this? I would say pull-ups could work if you have a bent upper back for example (thoracic kyphosis posture), but it really depends on the cause of the problem... It can be anatomical, but it usually isn't the problem. The problem is usually in the way people live: sitting for hours, too little movement etc. The body can adapt to what you're doing pretty good, meaning that if you train for strenght, you can easily get pretty strong and muscular, while sitting in your chair for most days and not moving causes your body to adapt to that specific posture (shortening the muscles in the front of your hip due to the sustained 90 degrees flexion that you have while you sit, etc).
Keep in mind that there's several diffirent reasons why posture can be bad.
- postural adaptation, which I described before. This is due to shortening of muscles that are always in a shortened position and lengthening of the stretched muscles and ligaments. This is what the article is about mostly.
Along with this, there's also little control of the deeper muscles that stabilize the spine.
Other causes:
- joints that are locked, limiting motion and causing pain
- anatomical variations limiting motion / causing pain
- some pathologies and nerve damage, but you'd probably visit a health care professional if this is the problem, as it can cause big problems.
What's interesting about the adaptation of your body: once one part of your body adapts, changes will appear in your whole body. This is why a very hollow lower back also causes a forward head posture
Anyway, if you want me to answer specific questions: the easiest way for me to help any of you is by sharing a few pictures of yourself in your normal, fairly relaxed posture. One taken from the side, one from the front and one from the back. That way I can see what your posture really is and give advice based on what I see.
Still it only gives me SOME info but just enough to share general advise... a more thorough conversation and even assessment might be needed to give a adequate personal advice. The general advise should work for >90% of the population and won't hurt you though, so just say so if you want more info.
What you have to do (in general):
- find the cause of your problem (example: sitting all day long)
- change your behavior (example: walk more, go do some sports, etc)
- practise good posture: every day until it gets better
- do specific training for stabilization of your spine (core stability training) and muscle development
- do some stretches for the shortened muscles (in my example: for your hip flexors, etc)