PDF is a format, not a filing category. A warranty, a research paper, and a delivered proposal may all be PDFs, yet you will look for them for different reasons. Keeping every PDF in one large folder can make the collection harder to use as it grows.
Place each file with the subject or project it belongs to. Keep a delivered PDF near the editable source when the two are related. For a reference collection, choose a few broad subject areas and use descriptive filenames. You should be able to distinguish a document without opening several nearly identical files.
Separate identity from storage location
A filename can contain the subject, issuing organization, and a useful date. Decide whether that date means publication or receipt, and use the same convention within the collection. For documents with formal revision numbers, preserve those numbers rather than substituting your own vague updated label.
Keep a short index when the collection has documents you consult together. An equipment register can link to each item's manual, receipt, and warranty. A project index can identify the approved specification. This avoids encoding every relationship into a deep folder hierarchy or duplicating the same PDF in several places.
Be careful when renaming or moving shared files. Links in spreadsheets, notes, or other systems may depend on their location. Test important references after a change and tell collaborators where the authoritative copy now lives.
Check what search can actually find
A scanned PDF may contain page images without searchable text. Try searching for a distinctive visible word, and select a small passage to see whether text is available. If you apply optical character recognition, verify important names, numbers, and dates against the page image. Searchability does not establish accuracy.
Retain the original when making a transformed copy, particularly if you crop pages, change orientation, or compress the file. Inspect small text and diagrams after compression. A smaller file is not an improvement if the detail needed to use the document becomes unreadable.
Review obvious duplicates cautiously. Two documents with the same title may contain different revisions, annotations, or signatures. Compare the contents and status before removing one. For records governed by an organization's retention requirements, follow those requirements rather than an arbitrary age rule.
Finally, test the collection with a real retrieval task. Find the manual for one device or the exact proposal sent on a particular date. The time and uncertainty involved will show which names, links, or folder divisions need attention.
