Sometimes there’s no way around it — you’ve got to use an app. If you need to sign a PDF document from your Android phone, that’s simply how you’ve got to go — unlike iOS, which lets you create a signature using its built-in Markup app, you need to find a third-party source. There are a variety of apps available, but the most well-known is the free version of Adobe Acrobat Reader.

So if you want to be able to sign off on contracts and other PDF documents without having to grab your computer, here’s how to use the Android version of Acrobat to do it:

Download and install Adobe Acrobat Reader from the Play Store.
Sign in (or create an account); if you’ve just installed the app, you may have to go through a number of popups offering directions and advice.
Tap the “Files” icon at the bottom of the screen. It will give you access not only to files saved on your device (you will have to allow access to all files first) but to those saved on Google Drive, OneDrive, Dropbox, Adobe’s Document Cloud. You can also search for PDFs that are attached to Gmail.

I chose Google Drive. I was invited to access Google Drive and PDFs from Gmail using the same email account; I also had to give the app access to your Google account.
However you decide to go, choose your source and tap on your PDF file to bring it up in Acrobat. Then tap on the “Edit” icon in the lower right corner.

Select “Fill & Sign.”
Tap on the signature icon in the lower right corner (it looks like a pen nib) and select “Create Signature” (or “Create Initials” if that’s all you need).

You’ll get a “Sign Here” box in landscape mode with the options (above the box) to draw your signature, insert an image, or use your camera to photograph a signature drawn on paper. When you’re ready, tap on “Done” in the upper right corner.

You’ll be returned to your PDF document. Tap on the area where you want your signature placed. It will appear in a box; you can pull on the sides of the box to make your signature larger or smaller, or tap on the trash icon (that will also appear) to get rid of it. When you’re done, select the checkmark in the upper left corner.
And you’re done! In the future, when you go into “Fill & Sign” and select the signature icon, the signature you just created will be there to drop into your document. If you want to try again, you can tap the “minus” sign to the right of the signature to delete it.