When reading the content of a PDF file on the Internet, there are two ways to do this: either view it in the browser or download it. This operation can be configured in advance on Google Chrome. Likewise, it is possible, in Windows as in macOS, to change the application that will open your PDF files by default.
Steps
Method 1 of 4: Enable PDF viewing in Chrome

Step 1. Run Google Chrome on your computer
The browser is for a Mac in your folder Applications (or in the Dock) or for a Windows PC, in All applications menu To start up.

Step 2. Click ⁝
The symbol is in the upper right corner of Chrome.

Step 3. Click Settings

Step 4. Scroll down, then click Advanced Settings
The option is at the bottom of the page.

Step 5. Scroll down and click Site Settings
These parameters are in the section Privacy and Security at the bottom of the list.

Step 6. In the Permissions section, then click PDF Documents
The mention is rather at the bottom of the list.

Step 7. Flip the switch to OFF (

).
This is preceded by the mention Download PDF files instead of automatically opening them in Chrome. As long as the function is in this position, any PDF document is automatically displayed in Chrome and not downloaded.
Method 2 of 4: Disable PDF viewing in Chrome

Step 1. Run Google Chrome on your computer
The browser is for a Mac in your folder Applications (or in the Dock) or for a Windows PC, in All applications menu To start up.

Step 2. Click ⁝
The symbol is in the upper right corner of Chrome.

Step 3. Click Settings

Step 4. Scroll down, then click Advanced
The option is at the bottom of the page.

Step 5. Scroll down, then click Content Settings
These parameters are in the section Privacy and Security at the bottom of the list.

Step 6. Scroll down and click PDF Documents
This mention is rather near the bottom of the list.

Step 7. Flip the switch to ON (

).
As long as the function is in this position, any PDF document is automatically downloaded and not displayed in Chrome.
Method 3 of 4: Change the default PDF reader (Windows)

Step 1. Click on the Start menu (

).
It's in the lower left corner of the screen.

Step 2. Click the settings icon (

).
It is on the left side of the menu.

Step 3. Click Applications

Step 4. Click Default Applications
The mention is in the list on the left.

Step 5. Scroll down the screen
Click on the blue link
Choose default applications by file type. On the left you have the file types and on the right the default application to run these files … or nothing (+ sign).

Step 6. Scroll down until you see.pdf
There, next to it, you must have a default application, the one you want to change.

Step 7. Click on the default PDF reader
Let's say Google Chrome is the default application, click on Google chrome. A list of other applications capable of running PDF files appears.

Step 8. Click on the desired application
Here is ! That's it ! You have changed the default application which will now open all your downloaded PDF files.
Method 4 of 4: Change the default PDF reader (macOS)

Step 1. Press the Control key
Click on a PDF file from your hard drive. A contextual menu appears.

Step 2. Click Get Info
Rather at the bottom of the window, you read Open with and below, the default application that opens PDFs.
For example, your default app might be Preview

Step 3. Click on the drop-down list under the Open with label
A whole list of applications appears.

Step 4. Click on the application you want
If you want Chrome, select Google chrome or if it's already Chrome, take Acrobat Reader…, what you want.

Step 5. Click Edit All
A message asks you to confirm or not this change.

Step 6. Click Continue
By clicking on this button, you change the default PDF reader.