Adobe Reader not recognizing tif files

Why doesn't Adobe Reader recognize tif files?  I created a pdf portfolio using Adobe Acrobat X Pro.  I scanned a black and white document with my Canon flatbed and saved it as a tif file.  I am unable to import the tif file into the pdf portfolio and I keep getting a pop-up that adobe reader does not recognize that type of file.  Anyone else have this problem and find the solution?