When you import a course from Blackboard to Canvas, all the text, hyperlinks, and general structure of the course remains intact, but any files you added to the Blackboard course become unlinked in the Canvas rebuild. The files are there in Canvas, it’s just a matter of finding them. This can be quite tedious unless you know a little trick (one of those “Secret Technology Club” tricks): Use Ctrl-F / Cmd-F to find the missing file in the File menu.
Click on “Edit Page” to start. Then go to the file menu (right panel) and drill down to the “Home” directory. Now you’re ready to search.
Then use Ctrl-F (PC) or Cmd-F (Mac) to search for a word or two in the title of your document or file. When you find a folder that seems to contain those words, open the folder and see if the file is there.