When I attach a file from my documents with outlook the receipent cannot open the file. What am I doing wrong?

When I click on insert and select attach a file, then click on the file and open, it will put it in the email and send it, but the receipents cannot open it.  Also, it shows up as a grey box, when I copied the file, scanned it and then attached the scan it showed up as an orange box, and the receipents were able to open it?  What do I need to do differently?