I used Avenir Book in bold for some subheadings in a document. Attached are images of how it looked when I printed a hard copy yesterday, and how it looked when I opened the document today.

The headings in Avenir Book bold are "No Conjunction" and "Conjunction & Comma."

The document has existed on only one machine, printed with the same printer. And ostensibly, the font has not changed. It is still Avenir Book bold. (By the way, this font change has occurred throughout the document, not just this page.)

How or why would a font change of its own free will? Does anyone recognize the font from yesterday that was apparently masquerading as Avenir Book bold? Any help for this mysterious situation would be greatly appreciated!
Yesterday (Right).jpg Today (Wrong).jpg