By default, estimates in QuickBooks Online (QBO) are printed on Letter paper size. I'm here to help you customize your printer settings so you can print on your desired measurements, @cink78.

Firstly, let's update your Adobe Acrobat so that your software will receive security patches and provide fixes to any issues like this. 

At the same time, we can edit your form's paper size on the PDF preview page and click the Fit to Page icon. Also, you can follow the steps I'll provide below to change your printing settings.

1. On your preview page, click the Print icon. 
2. Go to the More settings dropdown.
3. On the Paper size dropdown, ensure that it's Letter. 
4. You can also edit the Scale to your preference. 
5. After ensuring everything is in order, click Print.

Moreover, since you've received an error message that tells you to correctly set up your printer, let's go ahead and resolve this issue by changing your printer's default paper size from your computer's settings. To do so, please follow these steps: 

1. Go to the Start button, then click the Gear icon.
2. Select Devices, then Printers & scanners. 
3. Choose the appropriate printer and then click Manage.
4. Once you're on the Manage your device window, go to Printer properties, then Change Properties. 
5. Click the Paper tab, and then choose the paper size you want to use. 
6. Select Advanced (It may be a button or a tab depending on the version of Windows you are using.)
7. Increase the resolution.
8. Hit Ok.

Please read this article for reference: Printer Is Configured to Use the Wrong Paper Size.

You can check out this article for guidance on what to do when your customer accepts your estimates: Convert an estimate into an invoice in QuickBooks Online.

I'll be here to assist you if you have additional concerns about printing in the correct paper size in QBO. Make sure to comment below or tag me in a post.