PDFs changing proportions when converting to JPGs

Some of my PDFs are changing ratios/proportions when converting to JPGs. I have a handful of 8.5x11 (2550 × 3300) files that will work perfectly and others that will stretch the proportions 8.5x11 (2134 × 2508-which changes to 9.36x11 when opened in Photoshop) when I convert in Acrobat. In Indesign, I have even copied and pasted the information/images into a file that does work, but it still creates this issue. I sometimes get something closer to the right size if I remove the images from these files, but that is not a solution. When I convert in Indesign directly to JPG, I get no issue with sizing. However, I might not always have access to the Indesign file. 

Is this a resolution image size issue in my files? The ones that convert fine are about the same size per file as the ones I'm having issues with.

Thanks