Can i use one currency - usd on my pdf invoice for my customer?

Welcome to the Community, Stella.

The feature to change the home currency is unavailable if you have already activated the Multicurrency in QuickBooks Online (QBO). However, you have the option to add currency and assign it to your customers. 

Kindly refer to the image below for a reference of how multicurrency looks in your customer's invoice:



To ensure that you'll get to use the specific currency for your customer's invoice, here's how:
 

1. In your QBO account, go to the Customers & leads and select Customers (Take me there).
2. Select New customer.
3. In the Customer information window, fill out the required information.
4. Select Payment and billing.
5. In This customer pays me with field, select the customer's currency. This is the currency that the customer uses to pay you for products or services.
6. Once done, click on Save.

For detailed information, kindly visit: Assign a foreign currency to a customer in QuickBooks Online.

Once the currency is assigned to your specific customers, you can then create an invoice.

You can also check out this article if you want to learn more about the multicurrency feature in QBO: Turn on and use multicurrency in QuickBooks Online.

Moreover, I'll also share this article that can serve as your reference to learn how to record payments received/made using the multicurrency feature: Receiving and making payment for a foreign invoice/ bill with a foreign currency.

Feel free to leave a reply if you have additional QuickBooks-related queries. The Community team always has your back. Have a good one.