To import PDF files, there are 3 ways:

1. iTunes file sharing
2. Cloud file service (Dropbox, Google Drive, iCloud Drive)
3. Open In

a. iTunes file sharing

Windows, macOS Mojave or earlier

You can transfer files from your PC.

1. Launch iTunes.
2. Plug your device via USB.
3. Select your device on the iTunes left panel.
4. Select the Apps tab on the right pane.
5. Scroll down to File Sharing.
6. Select piaScore.
7. Click on the “Add…” button or directly drag & drop documents(only pdf) on the list.

macOS Catalina or later

Please see the following.

Use the Finder to share files between your Mac and your iPhone, iPad, iPod touch - Apple Support

b. Cloud file service

If you use a cloud file service such as Dropbox, you can download files from Dropbox.

1. Tap "Download" on the top of catalog view.
2. Tap "Cloud" or any cloud service
3. Input your cloud service account information

c. Open In

You can download files from any other application (include Safari).
(Dropbox enables you to share files among PC / iPad via internet)

In case of Safari (Web browser):

1. Open PDF file in Safari
2. Tap PDF and show toolbar at the top
3. Tap "Open in piaScore" or "Open in..."
4. Transfer PDF file to Piascore