Not all PDF files allow text to be selected, copied, or pasted. This is often because the PDF’s creator has applied restrictions or security settings that disable text extraction. In some cases, the PDF may simply be a scanned image rather than actual text, which also prevents copying.
If you need to copy or edit the content, try opening the file in Adobe Acrobat and checking whether permissions allow editing or text recognition (OCR). If the restrictions are enforced, the best option is to contact the sender or the original creator of the PDF and request an editable or unrestricted version.
Alternatively, you can take a screenshot of the required section and open it in the iPhone Photos app (or Preview on a Mac). Using Live Text, iOS/macOS can recognize and extract text from the image, allowing you to copy just the part you need.
In short: when copy-paste fails, screenshots plus Live Text often save the day.