I'm not familiar with the Abbrevia components but assuming they give you a TStream for your compressed PDF, to save it to the database you can try passing it into a function something like this:

procedure LoadFromStream(const S: TIB_Statement; const ParamName: string; const InputStream: TStream);
var
  wStream: TStream;
  blob: TIB_ColumnBlob;
begin
  blob := S.ParamByName(ParamName) as TIB_ColumnBlob;
  wStream := S.CreateBlobStream(blob, bsmWrite);
  try
    wStream.CopyFrom(InputStream, 0);
  finally
    wStream.Free;
  end;
end;

Example call:

ib_dsql.SQL.Text := 'insert into PDF_TABLE (ID, PDF_FILE) values (1, :PDF_FILE)';
LoadFromStream(ib_dsql, 'PDF_FILE', StreamFromAbbrevia);
ib_dsql.Execute;

I'm sure you can streamline this, just an example, hope it helps :)