It is of course legal, but it's possible OP got deceived into an annual subscription when they thought it was monthly, as discussed 7 months back on HN: https://news.ycombinator.com/item?id=30222165
1: https://github.com/abatsakidis/PDFDeSecure
2: https://www.google.com/search?q=remove%20pdf%20copy%20protec...
3: https://github.com/wilfredwee/wilfred-TILs/blob/master/comma...