This font looks like a "thin" Open Sans, how they do it? Or maybe it's a different font?
There are actually a handful of different weights for Open Sans. This is most likely the Open Sans Light 300.
Since it's already pointed out there is a thin weight for Open Sans called Open Sans Light 300 there is actually a way you can create thin text within Illustrator.
Convert the text to an outline by:
A good video to watch about kerning is "Typography Tip To Help With Kerning" but you could adjust the kerning before converting the text to outlines.
EDIT: AS indicated by DA01's comment I would also like to address this method is not ideal for body text and it should be reviewed with a fine tooth if you plan on using this for Serif Fonts. Especially look at the Ear, Terminal, Tail, and Bracket.
It's a different weight. Fonts usually come with a variety of typefaces that vary in weight (thin, regular, black, etc.) and also include oblique/italic variants often times as well.
These different weights or styles aren't "applied" to a font as much as they are separate typefaces themselves. Meaning if you would like a typeface to carry a different weight you should have that typeface available to you at that weight.
While there are certainly means to "fake" the weight of a font (make it bolder, italicize it) it is usually not recommended as having the actual typeface at the weight is preferable because it was designed to be viewed at the weight that it is.
As jos.lemmons pointed out, the Open Sans font contains a variety of weights.
Many vector graphic apps let you control the stroke (line weight) that is used to draw a font. You can often change this size of the stroke to make a font heavier or lighter. Affinity Designer does this and I think so does AI.
For some apps, you need to convert your type to outlines first.
Adding a missing step in Darthvader's comment:
The outside path cannot be deleted if we dont expand appearance.
There is no solitary reaction for "any type of" typeface editing as well as enhancing the device, as positioned in the inquiry. All at once, any type of such procedure in virtually any type of tool will certainly make the most of more manual taking care of later.
In FontLab Workshop 5: Probably To Gadgets > Activities > Effects > Bold as well as additionally enter an adverse number. A lot more unfavorable the number, the more weight will absolutely be done away with.
In FontLab VI: Probably To Tools > Activities > Shape > Modification Weight as well as move the slider to a negative number ... Numerous various other gadgets will absolutely have other commands, or sometimes might be losing out on the ability absolutely.