If you want to open RMS-protected PDFs in Edge, it needs to turn on Internet Explorer mode.
To turn on Internet Explorer mode, use the following steps.
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In the address bar for Microsoft Edge, type edge://settings/defaultbrowser and then click Enter.
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Slide the Allow sites to be reloaded in Internet Explorer toggle to ON.
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Restart Microsoft Edge.
Internet Explorer mode is now enabled. It needs to enable "Reload in Internet Explorer Mode" to open PDFs with Foxit PDF Editor.
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Navigate to the website you want to view in Internet Explorer mode.
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Click the three dots in the upper right corner of the browser window.
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Select Reload in Internet Explorer Mode.
If you are on Microsoft Edge version 92 or earlier select More tools > Reload in Internet Explorer Mode
Then enable "Open this page in Compatibility view" and "Open this page in Internet Explorer mode next time".
BTW: Microsoft Edge 83.0.478.37 or later can open protected files directly, but also requires "Reload in Internet Explorer Mode" to be enabled.