Use tiffcp

Usage: tiffcp [options] input... output.tiff

For instance:

tiffcp *.tiff output.tiff

And you will have a resulting multipage tiff

Then tiff2pdf (a wrapper for ghostscript)

Usage: tiff2pdf [options] input.tiff

Source: https://stackoverflow.com/questions/11135405/how-to-merge-many-tif-files-to-single-tif-file

A multipage tiff needs a multipage viewer, like qfaxreader, but if you convert to pdf, resulting file can be more easily seen with pdf viewers