In some PDF files or sections of PDF files, text cannot be highlighted or copied. Below you can find a list of common reasons and solutions for this problem.
Secured PDF files cannot be copied or annotated
If a PDF file is secured, it's not possible to copy text from it or annotate it. Citavi displays a yellow lock symbol in the bottom left of the preview pane if a PDF file is secured. Citing text passages from these types of documents is unfortunately more difficult and requires a workaround.
Solution for secured PDF files
If you want to save quotations from a secured PDF file, you will either have to retype the text or photograph it and use a text recognition program.
You can also find ways to remove the protection online, but before you take such a step, you may want to ask yourself why the publisher decided to add the protection in the first place and if you really want to go against the publishing company's wishes.
Scanned texts cannot be copied or annotated
You also might not be able to copy text or annotate a PDF file if it contains scanned text. That can happen if you receive a copy of an article through interlibrary loan. The first page with your order might have text that can be copied but all other pages are simply a photograph of the article.
Solution for working with scanned texts
Open the PDF file with a program that can convert scanned images to searchable text (Optical Character Recognition). You can find this feature in the full version of Adobe Acrobat. Alternatively, search for an online service that lets you upload a PDF scan and then download the file with searchable text by using the search terms "online OCR". The text recognition quality can vary widely, and you might need to try a few different providers.
OCR program results usually will contain some errors. When copying texts that have undergone OCR, you will often see letters that were interpreted incorrectly.
Slanted text cannot be annotated
Occasionally, you'll encounter a scanned text that has undergone OCR but that still can't be annotated. This can happen if the text is not horizontal.
Solution for slanted text
Apply OCR again. A good text recognition program will recognize such problems and will correct the image's orientation.