We’ve informed our developer about this feature. He need some time to investigate it. We will reply to you as soon as we will have some more info.
Usually we place features to our roadmap and prioritize them according to the customer license type. Dependent on how strong you are interested in the GroupDocs.Viewer library we can prioritize this feature to be implemented in one of the closest releases.
In order to perform investigation, our developers require a sample document where ligatures are present. You’ve mentioned the PDF document you are working on.
Also please clarify your requirement. If the document has a, for example, word “file” with ligature, like “”, then the GroupDocs.Viewer should find it even without ligature, using the “” search-word?