This is not a mod, it's a text edit for a configuration file.

Go to your %localappdata%\PAYDAY3\Saved\Config\WindowsClient and open Engine.ini with any text editor, preferably with Notepad++.
Scroll down to the bottom, and paste following;

[/Script/Engine.UserInterfaceSettings]
ApplicationScale=0.9

You can change the value to your desired amount, though anything smaller than 0.9 will make some texts overlap in UI. If you don't care for small text errors, you can go for 0.8 to 0.6. Anything below is unusable, have too much overlapping, but you're free to try.

But if you feeling lazy, I've prepared it for you to download.

Text errors are extremely noticeable in chat and communication wheel.

Don't forget to include two blank lines I've put in the code brick, when you launch the game, some variables will be added to your Engine.ini so your text might be overwritten if you don't include blank spaces.

Also, don't make the file read only.

Thanks.