Using pdffonts statement.pdf :
The "F1" (or F2, F3, etc.) suffix is a generic label assigned by PDF-generation software when it cannot properly name the embedded font subset. Essentially, your software knows there is a font there, but it doesn't recognize its official name, so it calls it "F1." Common fonts often renamed this way include: Times New Roman Tahoma Why the Error Happens cidfontf1 font new
The phrase appears to indicate a shift away from legacy F1 constraints toward a new generation of CID-keyed fonts. Using pdffonts statement