I can't select or copy text in a PDF file

Some PDF files require you to enter a password before you can select or copy text. Ask the person who gave you the document for that password.

If the Password command is disabled, this document does not require you to enter one. Make sure you've selected the Text tool by choosing Tools > Text. If you still cannot select text, the PDF is probably a scanned PDF, which does not contain any text but rather an image that may look like text.