Hello,
as of today (the "PDF24 Editor" from the older answers no longer exists), use Merge PDF:
- Open the PDF24 Toolbox and choose Merge PDF.
- Add your files. Besides PDF files you can add images, for example scanned receipts.
- Drag the files into the right order and click Merge. Then save the result.
If you only need some pages of the files, choose Page mode under Method and click the pages you want in the new PDF.
For an Excel file, create a PDF of it first, for example by printing it to the PDF24 PDF printer and saving it, and then add it in Merge PDF.
This also works online: https://tools.pdf24.org/en/merge-pdf. The online tool also accepts Word documents and other files directly.