if I forward an email, the attached document disappear

Hello gsalute,

Let's start off by checking the helpful steps in this article to make sure the proper steps are being taken: Reply to, forward, or follow up on emails in Mail on Mac. Follow this guidance:

1. "In the Mail app  on your Mac, select a message in the message list.
2. To include just a portion of the original message in your reply, select the text to include.
3. If you select the top message in a conversation, all of the messages in the conversation are selected.
4. Move the pointer over the message header, then click one of the following buttons:

• Reply  to reply to just the sender.
• Reply All  to reply to the sender and the other recipients.
• Forward  to choose new recipients.

1. You can add or remove recipients as needed.
2. Add your text.
3. If you included the original message, vertical bars (called quotation bars) may appear next to it.
4. You can make your text appear as quotations:

• Add quotation bars to your text: Choose Format > Quote Level > Increase or Format > Quote Level > Decrease. This also changes the quote level at which selected text appears.
• Paste text as quoted text: Choose Edit > Paste as Quotation. 

1. If the original message contains attachments, decide whether to include them: 

• Include attachments: Click the Include Attachment button  in the toolbar of the message window or choose Edit > Attachments > Include Original Attachments in Reply.
• Exclude attachments: Click the Exclude Attachment button  in the toolbar of the message window or choose Message > Remove Attachments.
• Choose attachments settings for all replies: Choose Edit > Include Attachments With Replies, then select an option.

1. When you’re ready, click the Send button . 

If you prefer to always omit the original message from your replies, choose Mail > Settings, click Composing, then deselect “Quote the text of the original message.”

If these are the steps you are taking and the issue persists, please make sure to restart your Mac (Shut down or restart your Mac) and make sure it's fully updated (Update macOS on Mac). Once those are done, please test this issue.

Let us know if we can help with anything else at all or if this doesn't settle your issue so we can look into this further with you. Thanks and have a fabulous day!