How can I set an image inside a PDF have the same size as the original JPG

I have an image JPG (a portfolio piece) that I want to confert to PDF.  In general I entire PDF file will be that image. As result when I open the PDF the image inside is zoomed and it pixelates and I want it to be the original size as the JPG. I tried saving the JPG in Photoshop and Illustrator as PDF but the result is the the same. In Acrobat Document Properties I set the magnifation to "actual size" but again it doensn't work.

Please help me get the image in actual size inside a PDF file. I spent 5 hours strugling with that but nothing helped.

Thank you in advance.