Parses an unencrypted PDF, or an encrypted PDF whose user password is
empty. For encrypted PDFs that require a user- or owner-supplied
password, use parse_pdf_with_password.
Parses an encrypted PDF with a caller-supplied password. The password
is tried first as the user password, then as the owner password; if
neither authenticates, the function returns
PdfError::InvalidPassword. For unencrypted documents the password
is ignored.