To fill out a PDF document, you must first save the corresponding file on your PC.
If you have already opened the document in your browser, you can download the file by clicking on the "Download" symbol (the arrow pointing downwards) in the upper right corner.
If you have not selected a different location, you will find the document in the "Downloads" folder on your hard disk.
You can now open and edit the PDF document with a free PDF reader. All you have to do is click on the text fields to be filled in.
Once you have entered all the necessary information and completed the editing, you can save the file and then send it as an e-mail attachment.