PDF files are less accessible than web flat pages so PDFs should not be used without a flat page alternative. Make sure PDFs are altered to meet accessibility standards, you can check this using the accessibility checker in Adobe Acrobat Pro.
The PDF should have:
- correctly tagged content within Adobe (as headings, text, tables, images, etc)
- the correct reading order within Adobe
- alt text added to all images
- bookmarks for all main headings in the navigation pane and the PDF file set to open this pane automatically
- the language specified (usually English)