PDF preview does not render characters both multibyte characters and single-byte characters

Summary

PDF preview does not render characters both multibyte characters and single-byte characters.
Some pdf files are not rendered on PDF Preview in Confluence 6.1 and 6.2.

Environment

• Confluence 6.1.4
• Confluence 6.2.0
• Confluence 5.10.8 can render the characters

Steps to Reproduce

1. Attach the sample pdf file to a page. ( testpdf.pdf )
   
2. Save the page.
3. thumbnail looks good.
   
4. Preview the pdf file. no characters.
   

Expected Results

Characters are rendered normally.

Actual Results

All characters are not rendered in PDF preview.

Workaround

no workaround