Map every legacy PDF URL individually to its new location before a migration, the same as any other page — PDFs are frequently the most-linked-to content type externally, and skipping them in a migration plan breaks more real inbound links than any other content category.
Migration URL mapping often focuses on HTML pages and treats documents as an afterthought, partly because they are harder to inventory automatically. That gap is exactly where migrations lose the most external, hard-to-recover links, since a PDF is frequently cited or bookmarked directly.
Every PDF URL gets the same individual old-to-new mapping treatment as an HTML page, as part of the same SEO migration process, not a separate afterthought pass.
Verify a sample of external, third-party links to your old PDF URLs still resolve correctly post-migration, since these are the links you have no direct control over and cannot simply ask someone to update.
Largely yes, and they can carry real search visibility on their own, separate from any page linking to them. That is exactly why losing a PDF’s redirect mapping during a migration is a genuine loss, not a minor gap: the document may be ranking and driving traffic independently of the site around it.
A crawl of the current site combined with server log analysis usually surfaces documents a manual list misses, including older files no longer linked from anywhere but still indexed or bookmarked externally. Building that combined inventory before migration is worth the effort given how much external linking PDFs typically carry.
Especially there, since a scientific archive is usually the largest and most externally cited PDF collection on a pharma site, and the one most likely to be assembled and mapped in a rush. See scientific content hub for how large document archives are structured and mapped during a migration without losing that citation history.
Any inbound link or citation pointing to it stops working, and the search visibility that page had built up is lost rather than transferred to its replacement. A 404 also looks broken to any visitor who bookmarked or was sent a direct link, which is a common way PDFs get found.
Tell us about your document library and we will make sure it is mapped correctly through your migration.