how can I password-protect a PDF file?

I am running 10.10.3 Yosemite and am wondering how to password protect PDF documents that I've downloaded from websites before I email them on? Can this be done? Thanks!

Gday.

This can be easily achieved in OS X's Preview App.

Open the PDF with Preview, by double click or right click (⌃+click) the file and "Open With" and once open, goto the Preview>File Menu and when that is open, pressing the 'Option' button will bring up "save as" so click that.
You can now Name the PDF, but more importantly, down the very bottom of the Drop Down menu, you will see ENCRYPT. Checkmark that, and put in a Password. Then repeat the Password again, and click Save.

You now have a Password Encrypted .pdf file, which can be emailed to the recipient and along with the Password they will be able to view it.

PS: to get around the Save As the way I mentioned it above, when the file is Open, if you use the kb shortcut ⇧⌥⌘S this will bring up the Drop Down menu to save the Document . . . I find this easier and second nature, but still gave you the file menu way, because I don't know how computer literate you are

Try this service: PDFProtect It's supposed to be free for files up to 200 MB. Or you can use Preview as shown by member Tattoo.

OMG, you guys are awesome, thank you so much!! TattoedMac, that worked perfectly, thanks for the step-by-step instructions! Thrilled. And thank you chscag also - much appreciate your help and taking the time to respond! THANK YOU!!!

Glad to help...