>It is possible to copy a .pdf file using FILETOSTR()?

Sure, almost anything can be moved in and out through FILETOSTR(). Even JPGs or other binaries. Just make sure you extract them with STRTOFILE() adding a full path and file name then launch using ShellExec or similar, using the Windows association to the file's extension.

Note: You can even encrypt the memo file contents with the Crypto API for added security while in storage in the DBF/FPT if needed.