在什么情况下你需要该特性？ In what scenarios do you need this function?

Working with ´.pdf´ files is in many cases the same workflow for me as working with other internal notes. Having the possibility of previewing and pinning such files when hovering over a link to that file or when hovering over an annotation that was made inside the pdf and reflinked in a block. This would make the user experience with SiYuan even better.

描述可能的最优解决方案 Describe the optimal solution

This functionality already exists for hovering over internal links. This action shows a preview window which can be also pinned.
If it's technically possible, implementing the same functionality for ´.pdf´ files.

描述候选的解决方案 Describe the candidate solution

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其他信息 Other information

I've seen you are working on a feature for pinning a Tab. This could already be a partial workaround for the issue and make it possible to pin ´.pdf´ files.