Is there any way I can download all my posts from blogger?
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:
Save the file and then upload it where you need to.
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.