That's when PlainMerge helps. After inputting an Excel file and a PDF file, you can drag and drop the Excel headers into arbitrary positions or match them with native PDF form fields, and then ...

Apple's Shortcuts app lets me merge two or more iPhone photos into one shot with just a few taps, no third-party ...

Python library that reads JSON files of any size. The magic is in the Array and Object types. They load stuff from the file only when necessary. The library expects files to be opened in binary mode.