If you have Windows 10 on your computer and you need to underline words, phrases, or even entire paragraphs, be aware that you do not need to install any software third parties. The own Edge, the native Windows 10 browser, offers you this feature.
How to highlight a text in a PDF file in Windows 10 without third-party software
Accessing this feature of the browser is very simple. Just open the PDF file in which you want to take notes with the browser (this is the default Windows software for this task, but if you do not open it directly, click on the PDF, choose Open with, and then select Microsoft Edge).
Once the file is open, select the text you want to underline or highlight with the mouse. Just place the cursor at the beginning of the part to select, click and without releasing the button, drag on the text until the end of the part you want to select.
With the selection made, release the mouse button and you will see a new context menu with several options. Click on the first one which is represented by the icon of an underscore with the letter A next to it and finally choose the color you want to highlight the text.
When you have finished selecting all the PDF parts you need, click the Save icon in the browser's menu bar (the icon in the form of a floppy disk) or press the Ctrl + G key combination. Changes will be saved to the file. original with which you were working and when you open it again, underlined parts are always available.
If you highlight a part you do not need or whose color is incorrect, simply click on the highlighted part to change the color or remove the underline from the menu that appears.