Is there any way I can download all my posts from blogger?
You can use this tool called Blogger Backup. Its free and open-source.
How to save entire blog as PDF
If you want to save your entire blog as an awesome PDF file which people can read and enjoy instead of having a dull .xml file, use Blogbooker or follow these steps:
Step 1: Blogger dashbord>Settings>Posts and comments>Posts> Show at most Put show at most 999999 posts on the main page. (Any large number)
Step 2: View your blog website. Print it (Ctrl+P) and choose the destination as "Save as PDF". Click on 'Older posts' and repeat. (If you have a lot of posts you'd have multiple pages so you'd have to click older posts) You should have multiple PDF files.
Step 3: Go to PDF combine and combine your PDF files.
If what you're looking for is to take your blog with you, exporting it is the option; unless what you're looking for is to export only your posts.
To export your entire blog:
Exporting > From your blogger dashboard >
Settings > Under
BASIC Tab > The first block is
Blog Tools >
Save the file and then upload it where you need to.