I opened a PDF file in illustrator, and I noticed that it only created objects for some of the cells, example
I tried using using a trace, but I cannot seem to select the problem cells. How can I get Illustrator to recognize the remaining cells?
There are no cells in a PDF file, just graphics objects.
What you see is not a cell but a background color square. The original file has added white color labels to some of the items yes. It seems to be that they have set a white background while others have not. This is not an error in illustrator but jus something the original author did. You can simply not select what is not there.
Its a bit unclear what you expect The cells to do. They are just white colored squares. These cells have no bearing for the text or any other element they just sit behind the other elements. To view this choose View → Show Transparency Grid or hit ctrl+shift+D.
If you need to fill the background of a cell with a different color then i would:
Or just draw the squares manually.