Run script across multiple spreadsheets (googlesheet) - google-apps-script

Question

I'm currently running a script that takes a sheet, converts it into PDF and emails it out to an email address nightly. I am doing this across three separate spreadsheets. Instead of it running separately on each spreadsheet, I wanted to see if there was a to call each spreadsheet, and run the script once and attach all the PDFs into one email. It works great by itself, but I feel like it would make sense if I can have one spreadsheet run the function once and incorporate the other spreadsheets as well. Any direction would be helpful Thank you!
The script I am using is as follows
function PDFtoEmail() {
var email = "email#gmail.com";
var ss = SpreadsheetApp.getActiveSpreadsheet();
SpreadsheetApp.setActiveSheet(ss.getSheetByName('Schedule 1'));
var sheet = ss.getActiveSheet();
var subject = "Nightly Scheduled PDF";
var body = "";
var url = "https://docs.google.com/spreadsheets/d/SS_ID/export?".replace("SS_ID", ss.getId());
var url_ext = 'exportFormat=pdf&format=pdf'
+ '&size=letter'
+ '&portrait=true'
+ '&fitw=true&source=labnol'
+ '&sheetnames=false&printtitle=false'
+ '&pagenumbers=false&gridlines=false'
+ '&fzr=true'
+ '&gid=';
var token = ScriptApp.getOAuthToken();
var sheets = ss.getSheets();
var PDFtoEmail = [];
for(var i = 0; i < 3; i++){
var response = UrlFetchApp.fetch(url + url_ext + sheets[i].getSheetId(), {
headers: {
'Authorization': 'Bearer ' + token
}
});
PDFtoEmail[i] = response.getBlob().setName("Schedule.pdf");
}
if (MailApp.getRemainingDailyQuota() > 0)
GmailApp.sendEmail(email, subject, body, {
attachments:PDFtoEmail,
});
}

Answer 1

SpreadsheetApp.openByUrl() can open (for use by the script, they don't open in browser window) spreadsheets other than the one that is currently active. openByID is equally valid.
var sheets = [firstsheeturl, secondsheeturl,thirdsheeturl];
for(var i = 0; i < sheets.length; i++){
var ss = SpreadsheetApp.openByUrl(sheets[i]);
//code to do on all three sheets
}