QR code is blurry

This looks like a resolution problem to me. When you enlarge a small graphic, you don't increase necessarily the resolution of the image. Enlarging just spreads the existing pixels out over a larger area and you get blurry images.

The fix is to go to a higher resolution, sometimes much higher resolution, image.

Whether or not your software can actually do that is unknown.

Items the Mac thinks are TEXT are scaled up, and anti-aliased for pleasant transitions and smooth looking diagonals and pleasant character-edges when viewed on screen at scaled resolutions, for easy viewing.

Items that the Mac thinks are GRAPHICS are not fiddled with.

¿is it possible your QR code is inserted in the file as if it were a single large character of TEXT?

If so, that is a Bad Idea™, because the Mac will "fix it for you".

By the time it has made it into the document as a TEXT character, it is FAR too late to just fiddle with smoothing. You need to go back to the source document and fix the fundamental error of presenting a graphic as a large capital letter in a barcode font.

Make it into a graphic in the original document, (e.g., by screen-capturing a picture of it and placing the picture in the document) and your troubles will cease.

Both the other devices you mention also feature H-res, Hi-color displays subject the text-doubling for readability.

What happens when you enlarge the picture or the entire screen? In theory, that should at least reduce the anti-aliasing.

Like the very first code you posted, that one is INHERENTLY smeary and awful. It is not a screen resolution or display problem.

Yet you were able to post ONE crisp one above.

what is the difference? where did each come from?

is the problem in Browser-capturing these into a PDF from a web site? EXACTLY how was the smeary one processed that the crisp one was not?

what is the original form of the file you are viewing?

is the file you are viewing inherently a .pdf that you could DIRECTLY download?

it looks like Safari may be 'fixing' it for you to view, doing a bad web-to-pdf conversion.

No one disputes that the QR code is blurry. it has definitely been over-processed.

What I am trying to understand is, "EXACTLY what steps did you go through to get that file in its current condition."

For example, Did you take a screenshot to collect that download?

What is shown on web site documents is often already a .pdf file. If you download that pdf file DIRECTLY, using the download icon already on the screen, rather than first opening in Safari then downloading the screen, would it be any better?

You open it with WHICH Mac Application and it becomes blurry?

Preview? the Mac program INTENDED to read .pdf files?

I dragged the crisp image from you first post into the Preview icon. It stayed crisp. I asked Preview to print it, it looked fine.

What happens to it in Adobe reader, or whatever it is called these days?

If my posting is not relevant to your situation, just ignore it.