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, Pdf To Word 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
And that's it! So, now you have the PDF file that can be easily printed/bound/copied/etc. What about converting a PDF file from one encoding to another one? Well, the process involves converting the .png file into the .pdf file that is being output for printing to PDF, for example. For such conversion, you need to install Adobe's Free Viewer. As an alternative, you can install a PDF converter software and convert the PDF to another encoding.