How to search inside PDFs — even scanned ones

The short version: first check whether your PDF actually contains text — open it and try to select a line. If text highlights, any search tool can read it: press Ctrl+F for one file, or point Agent Ransack at a folder with *.pdf in the File name box. If nothing selects, the PDF is a scanned image and is invisible to every search tool until you run OCR on it — PDF24 and NAPS2 do that for free.

Step 1: Work out which kind of PDF you have

Every problem with PDF search comes down to one fact: there are two kinds of PDF, and they look identical on screen.

• Text-layer PDFs were exported from Word, a browser, an invoicing app, or anything digital. The words exist as actual text inside the file, so search tools can read them.
• Scanned PDFs came out of a scanner, a copier, or a phone camera. Each page is just a photograph. There is no text inside — only pixels — so every search comes back empty.

The 10-second test: open the PDF and try to select the text by dragging across a line. If individual words highlight in blue, you have a text layer — skip to step 2. If your cursor stays a crosshair or the whole page selects as one big image, it's a scan — you'll need OCR (step 4) first. (OCR stands for optical character recognition; our glossary covers the term in more depth.)

Real-world folders are usually a mix of both, which is why a search that finds some invoices but not others feels so random. It isn't — it's finding every text-layer PDF and skipping every scan.

Step 2: Search a single PDF (and one folder in Acrobat)

For one open document, every reader works the same way:

1. Open the PDF in any reader (Edge, Chrome, Adobe Acrobat Reader, Firefox — all fine).
2. Press Ctrl+F (or Cmd+F on a Mac), type your phrase, press Enter to jump between hits.

Less known: the free Adobe Acrobat Reader can search every PDF in a folder without opening them. That's enough for a few dozen files:

1. In Acrobat Reader, press Shift+Ctrl+F (menu path: Edit → Advanced Search).
2. Select All PDF Documents in, then pick your folder from the dropdown (choose Browse for Location… for anything not listed).
3. Type your phrase and click Search. Results list every matching file and page; clicking a result opens the PDF at the right spot.

Advanced Search also offers whole-words-only and case-sensitive checkboxes — useful when "tax" keeps matching "taxonomy".

Step 3: Search hundreds of PDFs at once

Acrobat's folder search gets slow and clumsy past a few dozen files. For a real archive, use a dedicated tool. (For plain text files in a single folder, our free in-browser File Finder can search contents too — but PDFs need one of the desktop tools below.)

Option A: Agent Ransack — no index, just search

Agent Ransack is our pick for occasional PDF digging because it ships with a built-in PDF filter and reads the text layer directly — no index required:

1. In the main window, type *.pdf in the File name box.
2. Type your phrase in Containing text.
3. Set Look in to your folder and click Start.

Matches appear with the surrounding line of text in the preview pane, so you can confirm hits without opening each file. In our testing it chews through a 2 GB folder of reports in a couple of minutes — fine for one-off searches, slower if you do this daily.

Option B: DocFetcher — index once, search instantly

If you search the same PDF library every week, an index pays for itself. DocFetcher is free, open source, and built exactly for this: right-click in the Search Scope pane, choose Create Index From → Folder…, point it at your archive, and let it run (expect roughly a minute per few hundred PDFs on an SSD). After that, queries return in under a second, with keyword-in-context snippets and a preview pane. The catch: it's a Java app, and the index needs an occasional rebuild when files change.

Option C: Teach Windows Search to read PDFs

Windows Search can index PDF contents if a PDF iFilter is installed. Windows 10 and 11 include a basic one, but if content hits are missing, install Adobe's free PDF iFilter — and make sure you grab the 64-bit build, because the old 32-bit version silently does nothing on modern Windows. Then check the setting: Settings → Privacy & security → Searching Windows → Advanced indexing options → Advanced → File Types, select pdf, and pick Index Properties and File Contents. Rebuild the index and give it a few hours. Our content-search guide for Windows walks through indexing options in full.

Step 4: OCR scanned PDFs so they become searchable

No search tool can fix a scan — the text genuinely isn't there. OCR (optical character recognition) reads the page image and adds an invisible text layer behind the picture: the PDF looks identical afterwards, but Ctrl+F, Agent Ransack, DocFetcher and Windows Search can all suddenly read it. Three free-or-included options:

1. PDF24 Creator (free, Windows): install it, open the Recognize text (OCR) tool, drag in one PDF or a whole batch, pick the language, click Start. It uses the Tesseract engine and runs entirely on your PC — nothing is uploaded.
2. NAPS2 (free, Windows/Mac/Linux): best when you're scanning paper yourself. Click OCR on the toolbar, download the language pack when prompted (Tesseract again), and every page you scan or import gets a text layer before you save the PDF.
3. Adobe Acrobat Pro (paid): open the file, go to All tools → Scan & OCR → Recognize text → In this file. Acrobat's engine handles poor scans better than free tools, and it can batch a folder via In multiple files.

For a mixed library, the lazy-but-effective move is to batch-OCR the entire folder once. PDF24 skips nothing and re-OCRing a text PDF is harmless in practice — just keep backups, since OCR rewrites the file.

What about macOS?

Mac users have it easier: Spotlight indexes the text of PDFs automatically, so Cmd+Space plus a phrase finds text-layer PDFs out of the box, and Preview's Cmd+F handles single documents. macOS Ventura and later even apply Live Text OCR to images in some apps, though saved scanned PDFs still need a proper OCR pass to be searchable everywhere. Our Mac file search guide covers Spotlight operators and the best third-party tools.

Troubleshooting

• Search finds nothing in a secured PDF. Password-encrypted PDFs can't be read by any search tool until they're unlocked — open the file, enter the password, and save an unlocked copy. Permission-restricted PDFs (open fine, but copying is blocked) also block text extraction in some tools; Agent Ransack and DocFetcher handle most of them, Windows Search often doesn't.
• OCR output is garbage. Quality depends on the scan: aim for 300 DPI, straighten skewed pages (NAPS2 has a deskew option under image edits), and set the correct language pack — Tesseract reading German with the English model mangles every umlaut. Faint thermal-paper receipts may never OCR cleanly.
• Some files match, others don't, and you can't see why. That's the mixed-library problem from step 1. Spot-check the misses with the text-selection test; the failures will almost always be scans or secured files. Batch-OCR the scans and re-run your search.
• Windows Search still ignores PDF contents after installing the iFilter. The index must be rebuilt before changes apply: Advanced indexing options → Advanced → Rebuild, then wait — large libraries take hours.

If you'd rather skip the fiddling, any of the tools in our free file search tools roundup will out-search Explorer on PDFs without touching the system index.

FAQ