Append output to existing multi-page TIFF file

[SargisParunakyan]

Hello. I have to convert png file to tiff, and add that file to another tiff. For instance i have one png file, and one tiff file with 3 pages. i'd like to convert the png to tiff and add it inside that tiff file.In other words that tiff file with 3 pages should be 4 pages after that.I know how to convert png to tiff but how could i add that coverted file inside of tiff???