Merge ID from two different dataframes

There seems to be something strange with your ID's if I am reading that PDF properly. A numeric ID of 1.03013e+12 is unusual to say the least. You may very well be running into numeric accuracy problems which may be what is giving you the millions.

I think we really need reproducible example (reprex) or at least some sample data. Have a look at

A handy way to supply sample data is to use the dput() function. See ?dput. Since you have relatively large data sets then something like head(dput(myfile), 100) for each data.frame will likely supply enough data for us to work with.