Start by logging into your website
Once you are logged in, you will need to ensure that you are in edit mode by looking at the top left side of the site.
When logged in as an administrator and in Edit mode, there will be an action menu on every module on the page. The action menu can be found by hovering over top of the small triangle 
that is located on each module.
Hover over the triangle and you will see the Action Menu. Choose to Edit Text.
Be aware that different modules will have different action menus. The picture shown here is the Text/HTML module which is the most common module for putting text on a page. Once logged in your text will be opened in an HTML editor.
Decide where you want to have the download link and type in the text as you want it. For example: "Click Here to Download". Select the text that you want to have linked and press on the Hyperlink button from the toolbar.
When you press on the button, the Link dialog will be displayed. Press on the "Browse Server" button.
Once you press that button, you will see the Link Gallery window. Choose "File (A File On Your Site)" File upload dialog will dynamically display.
Click on the link "Upload New File" and the "Browse" button will dynamically display. Click on the "Browse" button and select the PDF file from your hard drive.
Once the file has been selected, you need to press the link directly below the browse field "Upload Selected File". The file will then be uploaded to the server. If the file is big, the upload process will take some time. Once the upload is complete, the window will dynamically display the file you uploaded in the "File Name:" field.
All you need to do now is press the link at the bottom of the window "Use Selected Link" That window will go away and you will be back to the Link dialog. Press the OK button:
You PDF file is now on the server and linked to the body of your text. If you are done with your edits, scroll to the bottom of the page and press the "Update" button.
This process can be used for more than just PDF files, you can link up any file that is on the server, .PDF, .ZIP, .DOC, .XLS, Etc.
There are many ways to accomplish tasks on a Creative I.S. Dontnetnuke website. If you have a library of downloads, you would be better off using the Documents module or File Links... A topic for another tutorial.