On a Apple computer, the “Print” function of the “Preview” app includes the choice for printing the open file to PDF. This works for converting various picture formats to PDF. In fact, any open printable file can be printed as a PDF. If your objective is to make a PDF into a searchable PDF, Word To Pdf Conversion works. There are some “free” software listings on the Internet, but I can’t suggest one or another. On a Apple computer, if you just want to merge two or more PDF files, click theft-most icon above the main PDF window. There’s dropdown with several choices. The second is to open “thumbnails”. Click it; you get thumbnails of every slide in your PDF file. Do this with both of the files you want to merge. Drag thumbnails from one file to the other - in the order you choose. You now have the merged file. (This is probably identical in the Windows operating system.) HTH
Here's the UI for an attachment file. The ability to use Adobe Acrobat Reader from within PDF documents is a huge boon, especially if you're on Mac or Windows. With Word and PDF files being opened in both the Reader and PDF viewer, you will still be able to manipulate your files in Word, if you so choose. Here's the PDF viewer UI.