Choose a PDF to list, page by page, the fonts the document references.
The inspector opens the PDF with the pdf.js library in the browser and reads the font resources each page's content stream uses, listing the font names as the document stores them. Names beginning with six letters and a plus sign, such as ABCDEF+Calibri, mark a subset font — only the characters actually used were embedded. The listing shows the fonts the document references; embedding detail is limited to what the file exposes through pdf.js, and a font named here may be substituted at render time if it is not embedded.
What does a name like ABCDEF+Arial mean? The six letters and plus sign are a subset prefix. The PDF embeds only the glyphs it uses from that font, and the prefix makes that partial copy's name unique.
Why might a listed font look different when the PDF is opened? If a font is referenced but not embedded, a viewer substitutes a similar font on the local machine. The inspector reports the referenced name either way.
Is the PDF uploaded? No. The file is opened and read locally in the browser with pdf.js; nothing is sent to a server.