Photoshop also likes to open files at 72dpi by default unless you change that in the preferences. And when copying and placing, it will default to 72dpi (and it changes the dimensions of the file in proportion to 72dpi) it’s still a good file, but you must uncheck resample, ...and then resize it to 300dpi of the tis what you are using.
Also, like you and Stever were mentioning, if the file is not all the way in the document...and you open the document, it will be cut off. I often select what I want in the vector, and do a copy and paste into photoshop. Then, I can change to inches, and put in my size (usually exact same size). But that’s where I then up my resolution from the default 72ppi to 600ppi without modifying the art. Then, all text is crisp and clean, and everything is sooo much more easily selected and pulled apart for seps. (Always turn off anti-aliasing).
This first image below, shows you what you should not do. The programs recognize “page documents” that’s where your art should be. Within the document. I had a guy send me an art file the other day, and he for some reason moved the art off the page, (cuz it was white art) on a white background. So he moved it off so I could see it on that darker bra ground. But this then did not translate over when I opened it. It was all gone. Empty. So Illy and Photoshop don’t like to recognize stuff on the outside of the page when opening in another program.