If you are on a Chromebook computer, you might get some weird behaviors when you try to interact with your worksheet PDF if it opens in the default "Gallery" application. If you click in a type-able area and your text is vertically centered in the box, or if you have freezing problems with the PDF, you might need to open the PDF in "View" instead of "Gallery".
To do this, first make sure you've downloaded the PDF by clicking on the link in your Assignment Panel.
Then, when the file has been downloaded, make sure you click "Show in folder" for the downloaded file. (If you don't see the "Show in folder" link, you may need to click the little arrow in the upper-right of the download dialogue to expand it.)
Clicking this link should open your Downloads folder. From here, find the PDF and right-click on it. (Depending on your settings, this may mean doing a two-finger click on your touchpad.) On the menu that opens, go to the "Open with..." option, and select "View".
This should open the PDF in the Chrome browser, which should allow you to correctly edit text directly in the PDF.