You can easily block the Auto-Lock function while reading PDF files in PDF Expert 6. For this, launch the app > open a PDF file > tap aA on the upper toolbar > turn on Auto-lock toggle. After that, the iOS settings will be ignored so that you don’t need to ‘wake up’ your screen every time you work with files but may stop using them for some time.
To enable the option on your iPhone, open a PDF file > tap Actions > tap View Settings (aA) and turn on Auto-lock toggle.
To enable the option on your iPad, open a PDF file > tap Aa button on the top toolbar and turn the iPad auto-lock toggle on.