I can reproduce the issue in Edge browser. When I reduce the width of the iframe to some value, the PDF toolbar will disappear. I think that's an issue of PDF reader in Edge. We can do nothing except providing feedbacks to Edge team so that they can check it and improve the product. According to this doc, I suggest that you can send feedback through the Microsoft Edge Insider forum. Besides, you can also provide feedback by pressing Alt+Shift+I in Edge.
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Regards,
Yu Zhou