Invoice Maker shows in History when an invoice has been crated, sent, viewed or paid, or when an estimate/quote has been accepted.

When you send or share a document it shows Sent. Once it's recognized that it has been opened, the status changes to Viewed. When you export it (PDF, mass export) it shows Exported.
​You can see the exact date & time when a document has been sent or opened, when a payment has been added or removed.

History won't show Viewed when your client opens a PDF file that you've downloaded.

Also it won't show Viewed, when you send a document using via iPhone/iPad from own email app and the customer's email blocks tracking pixels

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