This error occurs when fonts are not embedded in PDF
- Always have 'Fonts Embedded' option checked on while exporting the file as PDF. This option is selected by default in Indesign CC.
- Make sure PDF/X-4: 2010 format is selected while exporting PDF from MS office applications
- Always use Gelato Print Preset ‘Gelato Standard 1.4 (PDF/X-4 Coated GRACoL 2006)'
- Keep ‘Preflight’ enabled in InDesign
- Check Preflight errors in the same window before exporting PDF
Note: Also, this issue occurs when files from MS Office are saved to PDF, and PDF/X-4: 2010 format is not selected. Refer here to know more