First thing to do if you want to add PDF or other file link to your page is to upload the file to an asset folder. You can find the assets folders from the folder icon on the upper right-hand corner:
Then select Media section from the top and navigate to the folder you want to upload the file. You can create a new folder if needed from the three dots next to the folder name. For example, here I have Career folder selected, so if I crearted a new folder it would be created under the Career folder.
Once you have the correct folder selected you can just drag and drop the file as indicated in the picture above or click from the upload icon/text and then select the file from your device. After the file has been uploaded you should see it under the folder (files are displayed on bottom of the folder section).
After uploading the file the next step is to add a link to your page. Depending on the page type you might have different places too add links. Most page types have a Main body area where you can add text, images and links - this is where you usually add links. However, if the page type you are using doesn't have a Main body area you can for example, add a editorial block and then in the block you have similar area to Main body to add links.
You can add the link to anywhere in the Mainbody area just by adding text or highlighting part of the text. Once you have highlighted the part of the text you want to add the link, you can click from the link button on the Main body menu as indicated in the picture above. Then from the "Create link" popup scroll a little bit down, so you can click from the "Select media" button. Then select the uploaded file from the folder and click ok, now you should see the file name next to the Media icon in the popup and to finnish the setup click ok.
Now the link is added and you would just need to publish the page. If you wanted to add link to a different webpage instead of a file you would just need to select "Page" instead of "Media" from the link popup.