The safest method. Visit the official GOV.UK shop. For a small fee (usually around £10-£15), you can purchase a PDF edition that is watermarked with your license. This ensures you have the most up-to-date version reflecting current law.
Because this is a copyrighted publication, free downloads from torrent sites or file-sharing forums are illegal and often corrupted. Here are the three legitimate ways to get your PDF.
I can provide you with some general information about the guide, but I won't be able to provide a direct download link to the PDF due to copyright restrictions.