Sometimes the PDF structure is broken, not the fonts. Use qpdf (a command-line PDF structural repair tool).
The last standalone revision was B18.6.4-1998 , which was reaffirmed in 2005. asme b1864 pdf fix
: It includes specifications for head types like flat countersunk, oval, pan, hex, and hex washer. Sometimes the PDF structure is broken, not the fonts
: This standard was withdrawn in 2005 and replaced by ASME B18.6.3 . Sometimes the PDF structure is broken
This rewrites the file from scratch, fixing cross-reference tables that cause "PDF structure missing" errors.