How to open PDF from a forwarded email or change a setting?

You may want to check your settings to see what setting your Mac has in place for Mail attachments

For MacOS 15: Change Account Information settings in Mail on Mac - Apple Support

Eg: says

: ... in the Mail app  on your Mac, choose Mail > Settings, click Accounts, then click Account Information."

Look through the options for the "Download Attachments" option:

"Mail always downloads media attachments (such as image, PDF, video or audio files) that you receive.

To have Mail automatically download other types of attachments (such as spreadsheets or zipped files), click the pop-up menu, then choose an option:

All: Mail always downloads these attachments.

Recent: Mail downloads only attachments of this type received within the past 15 months.

None: Mail doesn’t download any of these attachments."

"Mail downloads attachments you receive to a special folder in your home Library folder".

This may help you find and open the atttachment.

Then you can decide whether to keep or change the setting.

Can you save it to downloads and then open it?

Go to the email server and get it from there. While your at it after retrieve the email and .pdf delete the email.

Thank you for taking the time to reply :-)