Adobe Reader is the program most often used to open ".PDF" documents (PDF = Portable Document Format). Recently, Adobe announced patch releases for it's PDF reader, some of which are critical. What I fear are all the hackers that are going to try to scare you into clicking on their link because you "have an outdated PDF reader"! Do NOT fall for any site or email that says your product is out of date or you need a critical patch!
Here's how to check. I am displaying Windows, but for Mac it is basically the same.
Open the program, Adobe Reader, from your list of applications.
Once opened, on the top tool bar, click on Help, then Check for Updates.
If an update is available, then it will display that. Go ahead and click on Download and Install. You will need to close the program to complete the update (but the updater will tell you when you need to do that. You should see a "success" message once it completes.
If you want to confirm, just repeat the steps. Open Adobe Reader, click on Help, Check for Updates.
There are other PDF viewers available and many of these types of documents will open in your web browser, without the need for Adobe Reader being installed. However, if you want to install it for the first time, do NOT click on any links that pop up or come in an email. Go to https://get.adobe.com/reader/ and download from the original source. There are a couple of gotchas, like you may also see for Java when you install or upgrade that (See update article for more information). A new install may also attempt to get you to install other software:
These companies pay Adobe (or Java) to offer their software. I recommend you do not install the optional offers.
Adobe may even be pushing you towards it's own products:
You are under NO obligation to download these offers. Though I like the Chrome extension (see my article on browser extensions) be aware of the permissions you grant it. If you are uncomfortable with granting this, you do not have to install it.