The black box problem typically occurs when the figure or graphic has been copied and pasted into the document.
This can be corrected by deleting the image and then using the Insert > Picture > From File option inside Word.
If you do not have access to the original image you can either click on the image and Save Image As. Delete it and Insert it as described above.
If you have multiple images with issues, you can try to convert to a PDF on a MAC computer these do not typically have the same conversion issues. There are MACs available on the second floor of Evans Library in the Digital Scholarship Lab.