Combining a few PDFs — a cover letter and a resume, a set of scanned receipts, several signed contract pages — sounds like it should be simple, and mostly it is. The part worth understanding is that not all "merge" tools do the same thing under the hood, and the difference matters if the file needs to stay searchable or print cleanly.
Two different ways to merge
Some tools merge PDFs by rendering every page as an image and stitching those images into a new file — essentially the same approach as taking a screenshot of each page. This works, in the sense that you get one file at the end, but it throws away anything that made the original a "real" PDF: selectable text becomes an uneditable picture of text, hyperlinks stop working, and the file is often larger than it needs to be for what it now contains.
The other approach copies each page directly at the document-structure level — the actual text, fonts, and vector content move into the new file untouched. This is slightly more technical to build, but it's the version worth using whenever the source PDFs matter: anything with real text, forms, or links.
How to tell which kind of tool you're using
After merging, try selecting a sentence of text in the result and copying it. If that works, the tool preserved the actual document structure. If the "text" is really an image and nothing selects, the merge flattened everything into pictures — which may be fine for a batch of scanned receipts that were images to begin with, but is a real loss for a document that started out as genuine text.
A practical merge workflow
- Gather your files and decide the order they should appear in the final document.
- Merge them using a tool that copies pages directly rather than rendering them — this one does exactly that, so any selectable text in your originals carries over.
- Check the result — open it, confirm the page order is correct, and try selecting text if the originals had any.
- If the merged file is unexpectedly large (common when combining scan-heavy PDFs), run it through a compression pass afterward.