We have had reports with a problem uploading PDF files to Glow Blogs.
This issue is now fixed, here is an example 3 page PDF uploaded to blogs: Test PDF file
PDFs that are uploaded to blogs are linked to the image thumbnails of the pdf. This looks like the first page of the pdf.
The developers are investigating a fix which we will be implemented as soon as possible.
We have a workaround at rather kludgy workaround.
You can upload pdfs somewhere else on the internet and link to them in your blog.
The O365 OneDrive provide by Glow is a good place to do this. After uploading a PDF to one drive you can ‘share’ it. Make it public and copy the link. In the blog post you want to add the pdf to you can, instead of uploading the file, link directly to it like this: Download Test PDF