A scanned PDF has no text to search: each page is a photograph of words, so Find has nothing to match. Try to select a word — if nothing highlights, that’s the reason. OCR reads the pictures and adds an invisible text layer, after which search, selection and copying work in every viewer.
Runs in this tab, on Tesseract (WebAssembly), pdf.js and pdf-lib, so your file is read from your own device and never sent anywhere. Check it yourself
How do I fix it?
1Check whether there is text at allDrag across a line, or press Ctrl+A (⌘A on a Mac). If nothing highlights, the page is a picture. If text highlights but copies as symbols, it’s the unreadable-font case.
2Run the PDF through OCR PDFPick the language it’s written in and press Make searchable. Each page is read on your device and an invisible text layer is laid over the words; the page itself looks exactly as before.
3For the garbled-text case, read every pageUnder Advanced, turn off “Skip pages that already have text”, so pages whose existing text is unreadable are read again.
4Search the new copyOpen the saved file and press Ctrl+F. Search, selection and copying now work — in Chrome, Acrobat, Preview and on phones.
Why does this happen?
The pages are pictures of text. A scanner or a phone camera saves what it sees as an image. The words are pixels to a PDF reader, however sharp they look.
The file was flattened into images. Some converters and compressors turn every page into a picture to force the file smaller or to “lock” it. The text layer goes with it.
The text was turned into outlines. Design software can convert letters into drawn shapes so a font never goes missing. They print perfectly and can’t be searched.
The text is there but unreadable. A font without a proper character map makes copied text come out as symbols, and search can’t match it either. It looks searchable and isn’t.
Questions
Why does Ctrl+F find nothing in my PDF?
Because there is no text in it to find — the pages are images. OCR adds the text; nothing else can, short of retyping the document.
Will OCR change how my PDF looks?
No. The recognized text sits invisibly under the picture of each word, so the pages look the same and only search and selection change.
How accurate is it?
On a clean, straight scan of printed text, nearly every word. Handwriting, faint copies and photos taken at an angle do worse, so check any figure that matters against the page.
Is it safe to OCR a confidential scan?
With OCR PDF, yes: the text reader runs in your browser, so the pages are never uploaded to an OCR service.