Look at the Help file in your copy of Acrobat DC / Reader for information about opening a PDF from your Mail app.
Would you provide more details about what you are trying to do?
You said that you wanted to "create" or "convert" to a PDF file.
What is the format of the receipt? Do you mean converting an email to PDF on your iPhone or something else?
Acrobat DC for iOS itself is a PDF viewer that offers the basic functionality (viewing PDF documents, adding annotations, filling out forms, searching, printing, sharing documents, etc.) for free.
To create PDF documents or covert one file format to/from PDF, you would need the Adobe PDF Pack online subscription service.
The following page lists the supported file types.
Unfortunately, there is no direct way to convert an email (in Apple Mail) to PDF on iOS.
Here are some alternatives that I can think of.
- Copy and paste the email content to a Word document and convert it to PDF with Adobe PDF Pack.
- Take a screenshot of an email on your iPad/iPhone and convert the image to PDF with Adobe PF Pack or other free/paid scan iOS app.
- Install the 30-day free trial version of Acrobat Pro DC (desktop app) on your desktop computer and print an email to PDF by choosing Adobe PDF as a printer.
Hope this helps.