Cannot extract the embedded font 'Foobar'. Some characters may not display or print correctly.
You may see this error with Adobe Acrobat 8 when you open certain PDF documents. If the Foobar font has been used all over the PDF, all you see of the document will be gibberish!
Adobe says they have fixed this error in their Acrobat 8.1.1 update:
1572280 Type 3 fonts with missing operators. PDF documents that contain Type 3 fonts with missing operators are non-compliant with the PDF specification. These non-compliant PDF documents are typically generated by third party products. When trying to opening the document, users see an error message, "Cannot extract the embedded font 'F0'. Some characters may not be displayed or printed correctly." PDF documents open correctly in Reader/Acrobat 7.x, but not 8.0 or 8.1. The root cause is Type 3 fonts that do not comply with the PDF specification, which requires either the 'd0' or 'd1' operator in every Type 3 character procedure. In version 7.x, if the offending character was not displayed, the PDF document opened normally. Version 8.0 catches this error even if the character is not displayed. The updated behavior will ignore the missing operator when the character procedure is empty.Root: fixes an issue in versions 8.0 and 8.1, not present in earlier versions.
However, installing the 8.1.1 update does not really fix this error! In fact, even though I incrementally updated all the way up to 8.2, the error is not solved. 8.2 is the last Acrobat 8.x update available for the 8 series.
There does not seem to be any solution to this error by Adobe. It does not seem to be fixed even in the 9.x series of Adobe Acrobat (see Mark Kostka's comment below). The solution seems to be the latest versions of Adobe Acrobat Reader or Foxit Reader. The PDF documents display and print without any problem in these readers!