If you would like to convert an HTML email to PDF, you can open the email in a print view (not sure what email client you're using, but if it's web-based, there's usually a printable version view), then hit Print and find the PDF option to save as a PDF.
If you want to send the HTML file, they are readable in any browser, e.g. Internet Explorer, Chrome etc.
Converting an HTML File To A PDF File
vba - Export html content to pdf using Microsoft Edge - Stack Overflow
How a can convert all file html to pdf at one time run start edge.exe
[Sharing] Convert HTML to PDF by Using Microsoft Edge in C#
Videos
If you would like to convert an HTML email to PDF, you can open the email in a print view (not sure what email client you're using, but if it's web-based, there's usually a printable version view), then hit Print and find the PDF option to save as a PDF.
If you want to send the HTML file, they are readable in any browser, e.g. Internet Explorer, Chrome etc.
Conversion is normally done by printing it.
There a few programs available that install an extra printer on the system. Because most items on screen can be printed to paper you just change the destination in the print dialogue, some give a few options to choose then you set a filename and destination. The "printer" then creates a PDF.
CutePDF, Bullzip and PrimoPDF are 3 examples.