What a free merge app usually costs you
The merge itself is not the product. A free PDF app has to pay for the servers it uploads to, and it does that in ways worth knowing about before installing one.
None of that is necessary for the job. Merging is arithmetic on a file, and the phone in your hand is more than capable of it.
- Storage permission across your whole device, when the task needs access to two files you chose.
- Your document on their server. Most free merge apps upload, process and send back — which is the part that costs them money and the reason the ads exist.
- Ads between every step, and often a watermark on the output unless you subscribe.
Saving to Drive instead of Downloads
The merged file lands in Downloads by default. To put it in Google Drive, open it from the notification or the Files app and use Share, then Drive — the file is already on the phone, so this is an ordinary upload you are choosing to make.
Selecting source files directly from Drive works too: the Android picker includes Drive as a provider. Large files are fetched to the phone first, so give it a moment on a slow connection before the file appears in the list.