Organize files before uploading
If you have many files, do not rely on a random upload order. Name them with numbers such as 01-cover.pdf, 02-report.pdf, and 03-appendix.pdf. You will know the intended order before you even open the tool.
Check for duplicates
It is easy to have both an old and an updated copy of the same page. Before merging, check filenames, sizes, and modification dates. One duplicate page can make the final document confusing even when the merge itself works perfectly.
Do not forget covers and contents pages
If the final file will be sent to another person, let the first page explain what the document contains when that makes sense. For long documents, a simple contents page can save the reader a surprising amount of time.
After merging, do not leave immediately
Open the first page, a page in the middle, and the last page. Make sure the page count makes sense and that the orientation has not changed unexpectedly. If the file will be printed, check margins and page numbers too.
The point is the final document
Merging is not only about putting files behind one another. It is a chance to turn a scattered set of documents into one understandable file. A minute of organization before merging often saves several minutes afterward.
Recheck page numbering and internal references
If source files contain printed page numbers or references such as 'see page 12,' the new merged order can make those references inaccurate. Review them in long formal documents. The merge can be technically perfect while the document itself still needs a page number or reference updated.