I want to make animation of wind that blows text in particles from top to bottom, but the wind blows the whole text. I think wind applies everywhere. How to control its area to blow specific things?
You could use falloff for the force field which will specify the shape of the areas where it will make the effect.
In the force field options (in the Properties editor) find Faloff area and check Tube instead of Sphere, selected by default. This will make force field affect in the areas which fall in that shape while with Sphere it affects radially in all directions.
Then enable Maximum, just below the Tube option; this will ensure the force field doesn't affect all the particles in the given area.
If testing this now, force field will affect all the particles in the given direction up to the specified minimum:
Particles are red icospheres; blue line in the middle is the plane which shows maximum area of the force field effect; partially transparent blueish cylinder shows force field shape itself.
This is however not what is desired; the force field affects up to the certain area, but to all the particles, reaching its minimum distance. To make it affect only particles within its shape of effect enable Maximum in the Radial settings:
With that, force field will affect particles up to the certain area (shown as blue line) and within certain area of the tube (in this case) shape.