Oops, I think ycarry above has the best advice.

I didn't read that "They're pencil sketches" closely enough - does that mean that those sketches were scanned in and are bitmap data?

MoI will only read vector curve data (things like lines, circles, drawing objects) out of AI or PDF files, not bitmaps.

To bring in a bitmap you need to put it in an image format like PNG and then use the View / Image command to bring it in as a background bitmap.

The File/Open and File/Import commands only deal with bringing in structured vector drawing objects like lines and curves, not bitmap/pixel data.

- Michael