Merge PDF

Order is decided before you merge

The file list order becomes the page order, and there is no undo once pages are combined. Read the list back against what the finished document should look like before pressing merge.

Files do not always arrive in the order you selected them - browsers sort by filename, and "page2.pdf" sorts after "page10.pdf" under most sorting rules. Naming files with a leading zero (01, 02, 03) makes them sort correctly in every tool you will ever use.

Password protected files must be unlocked first

An encrypted PDF cannot be read by any tool until its password is removed, merging included. You get a message naming the file rather than a silently broken result.

Unlock first, merge, then re-protect the combined document if it needs to stay confidential. That order matters - protecting first and merging second does not work.

Mixed page sizes survive the merge

Merging copies pages as they are and does not resize anything. Combine an A4 report with a Letter scan and the result genuinely contains both sizes, which printers frequently handle badly.

If the merged file will be printed or bound, run it through the page size converter afterwards. If it will only ever be read on screen, mixed sizes are harmless.

Quality is unchanged

Nothing is re-compressed. Text stays vector, images keep their original resolution, and the merged file is roughly the sum of its inputs. If the result is too large for where it is going, compress it as a separate step afterwards.