What is a PDF file and how do I make one?
PDF (Portable Document Format) is a widely used standard, which lets electronic documents be viewed and printed across a wide range of computer systems. Once PDF attachments are accepted by HMRC they can't be changed by either party.
There are various software applications for creating PDFs available. An internet search for PDF should provide links to the software products available, some of which are free to use. You will need to decide which one is most suitable for your needs.
Get help with PDFs.