Usually, you cannot copy a text from a scanned document in PDF format. But there's a way to extract it and you don't need an internet connection to do this like Using Free Online OCR Service. Given Adobe Acrobat is already installed on your PC.
- Open your scanned document saved as PDF.
- Press CTRL + A.
- Right-click and click "Recognize Text Using OCR" another window will open choose "All pages" and click the OK button. Wait for a few seconds/minutes to generate output. When generate output is done, you can now copy the text you want.