What happens to the pages
A PDF is a list of pages, and merging copies the pages you picked from each file into a new file, one after the other. The pages themselves are not redrawn or recompressed: text stays text, so you can still select and search it, and photos keep exactly the quality they had. Pages of different sizes and orientations can sit in the same file, each one keeps its own size.
A few things belong to the whole document rather than to a page, and a new file does not inherit them. Bookmarks (the outline in the side panel of a viewer) are not carried over, and neither are links that jump to another place in the same file, because that place may no longer exist. Fillable form fields keep their look but stop being editable. The title and author of the originals are left out. Links to websites, highlights and comments stay on their pages.
Choosing pages and their order
You do not have to use every page. Each file has a box for the pages to include. Write single pages and ranges separated by commas, like 1-3, 5, 8-, where 8- means page 8 to the end. You can also write odd, even or last. If you make a mistake, the box tells you which part it did not understand and how many pages the file has.
Choose pages opens a grid with a thumbnail of every page. Tick the pages to keep, drag a page to a new place, or use the arrow buttons on it, and rotate a page that was scanned sideways. The box and the grid stay in step, so you can start in one and finish in the other.
Files that cannot be merged
Password protected and encrypted PDFs cannot be merged here. Their pages are scrambled until they are decrypted, and ClipLime does not decrypt files. A PDF that opens without a password but has permission settings (for example no editing) is encrypted too, and is refused for the same reason. If you are allowed to, open the file in a PDF viewer, print or export it to a new PDF without protection, and add that copy instead.
A file that is damaged or only partly downloaded is reported with its name, so you can remove it and merge the rest. Scanned PDFs merge like any other, but a scan is a picture of text, so it stays unsearchable: ClipLime does not read text from pictures.
Big files and your device
The merge happens in your browser, so the limit is your device's memory rather than a fixed number of files. The files are read, copied and saved one after another, and the peak use is about three times their combined size. On a computer, sets of around a hundred megabytes merge without trouble. ClipLime shows a warning when the files add up to a size that is likely to be too much for your device, which is about 60 MB on a phone and a few hundred megabytes on a computer, because beyond that the browser can run out of memory and stop. A single file above 1 GB is refused for the same reason.
If that happens, nothing is lost and nothing was sent anywhere: merge in two steps instead, joining half of the files and then joining the result with the rest.