I understand the importance of creating a purchase order from an estimate window in QuickBooks Desktop (QBDT), sstiening. I'm here to share insights about this. 

If the purchase order feature is turned on, we can perform the verify and rebuild tools to locate and fix common issues with your company file. First, let's make sure that you have updated QuickBooks Desktop to the latest release to keep your software up-to-date so you always have the latest features and fixes..

Here's how to verify data:

1. Go to the Window menu and select Close All.
2. Go to the File menu and click Utilities.
3. Select Verify Data.

To rebuild your company file data:

1. Go to the File menu, select Utilities, and click Rebuild Data.
2. Select OK.
3. Choose where you want to save your backup and click OK.
4. Enter a new file name and select Save.
5. Click  OK when you get the message Rebuild has completed.

If the issue persists, I recommend running the QuickBooks Tool Hub. This will fix common issues in the program.

Here's how:

1. Close your QuickBooks.
2. Download the most recent version (1.4.0.0) of the QuickBooks Tool Hub.
3. Open the downloaded file. (QuickBooksToolHub.exe)
4. Perform the steps to install and agree to the terms and conditions.
5. Once done, double-click the icon to open the tool hub.

I'll also include this article to find more ideas on fixing data problems in your file: Fix common problems and errors with the QuickBooks Desktop Tool Hub 

Additionally, I've added this article about pulling up reports about open Purchase orders in QBDT: Create a report of your open purchase orders. 

 Feel free to ask if you have questions or concerns about creating a purchase order from the estimate window in QBDT. I'm always here to help. Have a great day.