Either the PDF carries a restriction that tells readers to refuse copying, or the page is a picture with no text in it. Try selecting a single word: if you get a blue box over the whole page, it is a scan. If nothing highlights at all, it is a restriction.
1Test what kind of PDF it isDouble-click a word. A word highlights on a real document; a whole page or nothing highlights on a scan.
2If it is a restriction, clear itUnlock PDF Restrictions rewrites the file without the permission flags, in your browser. No password is needed when the file already opens without one.
3If it is a scan, it needs OCRText has to be recognized from the image before it can be copied. That tool is in the next wave here; meanwhile, most scanner apps and Acrobat can add a text layer.
4If it pastes as gibberish, copy from a different readerChrome’s built-in viewer and Preview sometimes map glyphs where others fail. Otherwise the text has to be recreated, because the mapping the file needed was never written.
Why does this happen?
The file has copy restrictions. An owner password can mark copying as not allowed. The document opens normally, but your reader greys out copy and extract.
It is a scan, not a document. A scanned or photographed page is an image. There is nothing to select because no characters were ever stored — only pixels that look like them.
The text is in a form field or annotation. Values typed into fields and text inside sticky notes are separate objects, and some readers do not let you select across them.
The fonts have no character mapping. A badly made PDF can embed fonts without the table that says which glyph is which letter. Text selects, but pastes as gibberish like "☐☐☐".
Questions
Is it legal to remove copy restrictions?
For your own documents and files you were sent to read, yes — it is the same as saving a copy. A license that says you may not redistribute the content still applies, whatever the file allows.
Why does the PDF open fine but not let me copy?
Because that is exactly what an owner password does: it leaves the document readable and marks copying, printing or editing as not allowed.
Can I copy text from a scanned PDF at all?
Not until it has a text layer. OCR reads the letters from the image and stores them behind the page.