Helping you send invoices with a PDF file attachment is my priority, JFazz.

Updating your QuickBooks Desktop for Mac to its latest release is a good start when it comes to fixing data-related issues. Here's how:

1. From the QuickBooks▼ drop-down, select Check for QuickBooks Updates.
2. If a newer version is available, select Install Update.
3. When prompted, select Install and Relaunch.
4. Once the update is complete, QuickBooks for Mac automatically opens.

Once done, go back to your file menu, make sure the ATTACH PDF option is selected and send a sample invoice. If it's still not attaching the PDF file, let's repair your Adobe Reader by following the steps below:

1. Close Acrobat/Reader and all open web browser windows.
2. Select the Start button at the bottom left of your screen.
3. Type Control Panel, then press Enter. Go to Programs and Features.
4. Select Acrobat or Adobe Reader, then Uninstall/Change.
5. In the Setup dialog box, select Next.
6. Select Repair, then Next.
7. Tap Install.
8. When the process is complete, select Finish.
9. Restart your computer and try sending invoices again.

Additionally, you can visit this file to know what's new in QuickBooks Desktop for Mac 2021: QuickBooks Desktop Mac 2021 User’s Guide.

Let me know if there's anything else that you need about this or with QuickBooks. I'd be happy to help. Have a good one!