Image quality kind of decreases when adding to PDF

I'm using Adobe acrobat Pro DC and when I try to make png file in to pdf, the problem occurs.
Here's what I do
1) I have a png file of 1920x1080 resolution (it's a screenshot)
2) I open Adobe acrobat and use the "Organize Pages" function, select a file(png) and open it up

3) Save the PDF file created.

Now, the overall image quality, especially the text seem very unclear and dirty although the resolution remains the same.
Below is a comparison(upper one is the original)

Does anyone have similar issues? I didn't change anything in the settings, they're pretty much default. Thanks