1. PDFs aren’t support for viewing via transclusion in DEVONthink. See the Help image I posted previously. Obsidian has implemented a PDF viewer, as I also mentioned.
“Omnivore” is the group the MD file is in and the pdf is located in the “attachments” folder
2. Your path is incorrect regardless.
![[Omnivore/attachments/75ce0c2d-9b35-45ed-9f6b-76d93f273fd4.pdf]] would be linking to a document in an attachments sub-subgroup of an Omnivore subgroup of the group containing the Markdown document.
![[/Omnivore/attachments/75ce0c2d-9b35-45ed-9f6b-76d93f273fd4.pdf]] would link correctly if the Omnivore group was in the root of the database.