this upload of yours has not yet been officially added to IMSLP. You need to:
2) Once you've done that, go to this composer's page and click the link there to Add a piece to this composer page
2a) Give it a title such as "Quartet" and fill in any other info you know (the name of the composer will be supplied automatically)
3) Once you've done that, go to the page for "Quartet (composer's name)" and click on the link to Add a file to this page
4) On the next page, select the link where it says Use this form for files already uploaded
5) On that page, the filename you uploaded was Quatuor - Desenclos.pdf. Please fill in the other info and click Submit!.
It's often easier when you add a score for a well-represented composer such as Bach, Mozart or Schubert, when nearly every work has already been uploaded in some form, so you don't need to go through steps 1) and 2).