I have IrfanView 4.52 32-bit installed with all its plug-ins on a Windows 10 Pro 64-bit system.

After some tests, I found that I can open some but not all AI files with IrfanView. AFAIK it can open all EPS and PDF files of any size.

I wondered why it can open only some, but the most strange in this case is that, when I try to open some AI files the error message refers to PDF files! Check the video below.

I decided to import one of these "strange" AI files into CorelDRAW. I found out they were made (in a unknown app) with color images, fonts and perhaps some sort of layers. CorelDRAW showed that dialog about missing fonts, PANOSE, etc. and then imported the AI file, which BTW is a little bit messy:

Click image for larger version. 

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I guess this kind of complexity in the origin file somehow makes Ghostscript take it for a PDF file. Can it be a possible explanation for such error messages?