Hello,
PDF24 can now insert a clickable table of contents when you merge files. In the online tool Merge PDF (https://tools.pdf24.org/en/merge-pdf), add your files in the right order, click the gear icon (Additional options) and tick Insert table of contents. The merged PDF then starts with a page that lists each file with its start page, and each line is a link to that page. Create bookmarks additionally adds a bookmark for each file. These options are not available in Page mode. In the PDF24 Toolbox on the desktop, the same option will come with the next version.
So convert each part (e.g. each Word document or each piece of sheet music) to its own PDF and merge them with this option. The file names become the entries of the table of contents, so give the files meaningful names before merging.
Please note: the table of contents has one entry per merged file. A table of contents created from existing bookmarks or from the headings within one document is not possible yet. Thank you for the suggestion, we will add it to our list. If your booklet is a single Word document, you can insert the table of contents in Word before converting it.