Use PDF optimization (Acrobat Pro → Save As Other → Optimized PDF) → Check "Discard duplicate font subsets."

often appears when switching between Arial and Helvetica during creation. CIDFont+F1 issue - Adobe Community

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The next time you see these six mysterious fonts in a PDF report or prepress ticket, you will not see chaos—you will see a predictable, structured, and manageable system at work. And now, you know exactly how to handle it.

In the context of PDF and PostScript, F1 through F6 are (variables). They are keys used to identify which font is being used on a specific page or within a specific document. They are not the font names themselves.

Understanding CIDFont+F1, F2, F3, F4, F5, F6: A Guide to Troubleshooting Missing PDF Fonts

When a subset is created, the system needs to name it. If multiple subsets are created within a single PDF, the software labels them sequentially: CIDFont+F1 , CIDFont+F2 , CIDFont+F3 , etc.