Since the highlight rectangles are painted over (that is, overlap) the document layer, the background fill color must be transparent. For custom highlight colors, pass the required TdxAlphaColor values instead. Pass the dxacDefault global constant as the Highlights.Add procedure’s ABackColor and AFrameColor parameters, respectively to highlight a text range with the standard fill and outline colors. The PDF Viewer’s Find Panel uses the highlighting system to highlight the text matches it finds with the standard colors depending on the current look & feel settings. A highlight is a colored rectangle with its outline painted over a text range within a document. You can use highlight the returned text range using standard or custom colors by calling the control’s Highlights.Add procedure. Most of the search methods that the PDF Viewer control and the PDF Document object provide are functions returning a TdxPDFDocumentTextSearchResult value that stores the search result status and a text range corresponding to the text match’s actual position within the document (the text range is empty if the text search is unsuccessful).

The additional (fourth) overloaded variant allows you to search the text matches on a specific document page.

The PDF document object has four FindText overloaded method variants, three of which provide the same functionality as the control’s search methods. The control provides three overloaded TextSearch.Find method variants allowing you to search a specific text string in two different modes – that is, search through the entire document or search only the next (or previous, depending on the passed search options) search result at a time

The ExpressPDFViewer Suite provides an API for performing document search operations both at the PDF Viewer control and internal document representation levels: How to Search and Highlight Text in PDF Documents

How to search and highlight in pdf