To send PDF files from Safari to PDF Expert you can use 2 methods:
The PDF will be automatically saved and opened in PDF Expert.
You can also open a file from PDF Expert using the URI scheme in Safari. Type PDFEFILE:///Folder/Subfolder/File.pdf to open file.pdf stored in a folder/subfolder in the Documents tab within PDF Expert.
URL schemes can be used for files kept in Synced folders, in this case, please use the following URL scheme pdfefile:///SyncedFolders/folder1/folder2/test.pdf where pdfefile:///SyncedFolders/ is a static part.
Note: if you use the app in any other language, please use the translated version of Synced folders part of the URL scheme (e.g. if the language of your app is Japanese, the URL scheme will look like rdocs:///同期フォルダ/folder1/folder2/test.pdf)