{"id":2772,"date":"2026-06-22T16:54:18","date_gmt":"2026-06-22T16:54:18","guid":{"rendered":"https:\/\/gopdf.io\/blog\/?p=2772"},"modified":"2026-06-22T16:54:18","modified_gmt":"2026-06-22T16:54:18","slug":"adding-underlines-to-text-in-pdf","status":"publish","type":"post","link":"https:\/\/gopdf.io\/blog\/adding-underlines-to-text-in-pdf\/","title":{"rendered":"Adding Underlines to Text in PDF Documents"},"content":{"rendered":"

Underlining in a PDF can mean two genuinely different things, and confusing them is the root of most frustration. One is an annotation<\/strong> \u2014 a markup line drawn over existing text to flag or emphasize it, the digital equivalent of a highlighter pen. The other is a text-edit<\/strong>, where you change the actual character formatting so the underline becomes part of the document\u2019s content. Which one you need decides which tool works and whether the underline survives editing, copying, or printing.<\/p>\n

Annotation Underline vs. Editing the Text<\/h2>\n

An annotation underline sits on a separate markup layer. It\u2019s ideal for reviewing, proofreading, or marking a contract clause, and it can be removed cleanly without touching the underlying text. It also carries author and timestamp metadata in many readers, which is useful for collaborative review.<\/p>\n

Editing the text formatting changes the content itself \u2014 the underline behaves like underlined text in a word processor and moves with the words if the layout reflows. This requires a PDF editor<\/a> with true content-editing capability and only works on PDFs that contain real, selectable text.<\/p>\n

Methods for Underlining<\/h2>\n

Use the underline annotation tool<\/h3>\n

Nearly every PDF reader \u2014 including free ones \u2014 has a markup toolbar with an underline option. Select the text, click underline, and a line is drawn beneath the selection. You can usually change its color and remove it later from the annotations list. This is the fastest route and works without editing permissions in many files.<\/p>\n

Edit the text directly<\/h3>\n

In an editor with content editing, click into the text, select the words, and apply underline formatting from the text properties. This is the right method when the underline must be a permanent part of the document \u2014 a finalized form label, for example.<\/p>\n

Draw a line manually<\/h3>\n

When the PDF is a scan (an image with no selectable text), you can\u2019t select words to underline. Instead, use the line or drawing tool to place a straight line beneath the relevant area. Hold the shift key in most tools to keep the line perfectly horizontal.<\/p>\n

A Practical Workflow<\/h2>\n
    \n
  1. Determine whether the PDF has selectable text \u2014 try to highlight a word. If the cursor selects characters, it\u2019s real text; if it selects a whole block as an image, it\u2019s a scan.<\/li>\n
  2. For review and emphasis, use the annotation underline tool \u2014 reversible and non-destructive.<\/li>\n
  3. For permanent formatting, switch to a content editor and apply underline to the selected text.<\/li>\n
  4. For scanned pages, run OCR first if you need selectable text, or draw a manual line if you only need the visual mark.<\/li>\n
  5. Save a copy so the original stays intact, especially when annotations must be preserved separately.<\/li>\n<\/ol>\n

    Common Mistakes and Edge Cases<\/h2>\n