When text in a document isn't created as PDF Text, it doesn't get recognized in the app. This affects the ability to highlight, search, and other interactions with normal PDF Text.
For example, when you use our Text Box annotation in Drawboard PDF, because it's considered an annotation, it does not get saved as PDF Text but Annotated Text. It is almost treated like an 'image' instead of the text itself.
There's no way for Drawboard PDF to insert PDF Text at the moment.
A usual case where this might happen:
If you were to print this article from your browser using 'Microsoft Print to PDF' (which converts it to an image, then PDF) instead of 'Save as PDF'. You'd realize the whole document's text cannot interact with PDF Text tools. This also happens sometimes for scanned documents from some printers.