I'll make sure you can attach documentation or the invoice copy of your property tax bills on your Bill transactions in QuickBooks Online (QBO), @ERB-Pittsburgh.

You can add a copy of your property tax invoice as an attachment to your bill. This way, you'll be more organized with your record-keeping. Then, helps you in keeping your books accurate.

To attach a document to the bill, follow these steps:

1. Go to the + New button, then select Bill (if you haven't created the transaction yet). Open the bill transaction from the Expense menu if you've created one already.
2. Enter all the necessary property tax info.
3. Go to the Attachments section below, then click the box or the Attachments link to choose the file.
4. Select Save or Save and close once you're done. 

You can also attach a document to your customer and vendor profiles. Then, directly upload a file to the Attachments list without attaching them to a transaction or profile. To learn more about this, you can refer to this article: Attachments in QuickBooks Online.

Once bills are entered, you'll have to record payments towards them in QBO depending on how they're paid. Please check out this article for the complete details: Enter bills and record bill payments in QuickBooks Online (Record payments towards bills section).

Then, I'd recommend monitoring your business expenses by pulling up transaction reports (i.e., Expenses by Vendor, Transactions List by Vendor or Purchases by Vendor). To do this, go to the Expenses and vendors section from the Reports menu's Standard tab.

Also, I'm adding this article to further guide you in entering your expenses, paying bills, writing checks, and managing suppliers using QBO: Help Articles for Expenses and Vendors. It also includes topics about purchase orders, vendor credits, and managing inventories, to name a few.

Let me know if you have other concerns about managing business expenses and attaching documents in QBO. You can drop a comment below, and I'll gladly help. Keep safe always, @ERB-Pittsburgh.