If there are Unicode Glyphs missing on the server, you may see characters replaced with a question mark and if there is a font missing on the client, you may see characters replaced with boxes like in your case. Make sure that the font you use in the report supports the characters that would be displayed. For example when you use a font that does not support non-Latin characters, but then non-Latin characters are added to the report and it is exported to PDF, they would be replaced by question mark character (?) as PDF doesn’t automatically substitute fonts.
Note that the GDI font substitution in Designer Preview or rendering to HTML behaves differently than PDF.
To view the list of fonts that are embedded in a PDF file, open the file in Adobe Acrobat and from the File menu, view Properties. The Fonts tab displays the list of fonts that are embedded in the file.
For more information, visit Design Considerations for PDF Rendering
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