The problem is that the submitted pdf file does not embed some required fonts.
You can use Adobe Acrobat DC to perform the following operations on pdf files:
1. Select the print option
2. Enter the property page
3. Select edit in the default setting
4. Select the font, click the add name option to add the required font and save the configuration.
5. Finally, open the pdf that needs to be modified and print it to generate a new pdf.