Open the PDF in a PDF reader or editor that supports highlighting
Select the highlight tool
Choose the text or area you want to highlight
Drag across the text if highlighting text
Click or tap the selected text to apply the highlight
Adjust the highlight color if needed
Save the PDF to keep the changes
If using a browser or mobile app, use its built-in annotation tools
If the PDF is scanned, use OCR or a text recognition tool first
Reopen the file to confirm the highlight was saved