Choose a PDF, then drag across the text you want to underline — the line snaps to sit right under the words when you drag across real text. Over empty space, or on scanned pages with no text layer, the line is placed at the bottom of the region you drag, so drag snugly under the words there. Runs fully in your browser — nothing is uploaded.
Underline the sentence that decides it: drag across the text and the line lands neatly underneath in the downloaded file.
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Underline text in a PDF by dragging across it: a clean rule in indigo, black or red is placed at the foot of your drag and saved into the document.
A student underlines the thesis sentence of every source paragraph — by Friday the PDF itself shows the argument’s skeleton, ready for the essay.
When the page has a text layer, your drag snaps to the lines it covers and the rule is stored just under each line’s baseline; anywhere else, the rule sits at the bottom edge of the dragged region. Either way it is a thin filled rule in the colour chosen, stored as real PDF vector content. It prints crisply and adds virtually nothing to the file. Because placement is regional, it works on scanned pages too.
Yes — you are drawing a rule over a region, so scanned pages underline like any other.
On a text page that should not happen — the line snaps under the words. On a scan or over empty space, delete it with its ✕ and drag again, ending the drag where the line should sit — the bottom edge of your box is the line’s position.
No. It adds a graphic rule above the page content; the words remain original and selectable.
Yes — pick a colour, drag the lines for it, then switch colour and continue. Each entry in the list shows its colour.
No. Everything runs in your browser.