It simply means there's no PDF reader installed on your computer. Or if it's already installed, then there must be some default pdf reader recently set incorrectly to another application/program. If you are sure that there's a pdf reader, like adobe reader, foxit reader, etc..etc.. installed on your computer, follow the steps below:
Right click the pdf file (i guess you've downloaded the pdf file), click "properties",
there you'll see a "change" or "Browse" button on the general tab, click change or browse and locate the program to open the pdf file, select it and click "Ok" then "Apply", close the dialog box and double-click the pdf file, it'll open without any problem. You can also directly open the file on your internet browser like Internet Explorer, Google chrome or Firefox etc..etc.. Simply right-click the pdf file and select "Open with" and browse the internet browser and click it.
If in case you need a pdf reader to open the file, click here to download adobe reader
. Open the link, click "Download" proceed with the onscreen instructions and install the program, if you are asked to confirm whether this problem to be made the default pdf reader, confirm it and and finish the installation by clicking finish. Now open the pdf file, there'll be no more issues.
If you need further help, let me know, it would be much appreciated if you can let me know how you open the file.
Thanks for using FixYa.